Some good points with Elena's house gone, I think Jeremy will live in Matt's home while Matt is in Europe...I guess Jer should first live solo(you never know what new secret he's carrying, when he died the first time he could see ghosts, who knows what he can do now he may be some altered hunter with new abilities)

One player you forget is Tyler he is coming back and i think after learning of katherine's situation he may try and make hybrids himself.Now we only assume Klaus can make hybrids, it is not stated for a fact that other hybrids cannot. I mean vampires make vampires, why would hybrids be too different ..It all boils down to Tyler's motivation and ruthlessness .It would be nice to make him an anti hero this season who is really vengeful.Who knows he may have made a witch friend for extra protection from Klaus on his travels and will return with her so we have a new witch in mystic falls

I think Silas will be in MF , trying to protect Katherine..he has a vested interest if she is in fact a walking talking cure... Though i doubt suicide is his gameplan. Alternatively and it could be possible that when writers say Katherine will turn to an unlikely person for protection it could be either Caroline(who likes being the Florence Nightingale on the show and the fact that Katherine turned her would be really poignant) or to throw another triangle into our path she will turn to Damon and Damon will be caught between Elena and Katherine , but that will be quite taxing to pull off camera wise requiring Nina to play two roles in the same scene.I'd stick to Katherine seeking protection from Silas(who she thinks is Stefan) or Caroline.

I dont think Rebecca will stick around for long.However I have an idea how she could leave MF.It can be done if Matt was given a really big role like if he met an angel in Europe while with Rebecca who told him that he is chosen to be one like them and he was part of the key to curing vampirism, he tells him he can give him the ability to negate vampire powers which excites Matt coz he doesnt want to be compelled or turned by Rebecca. He gets white veins on his hands after the 'angel' grips his hand and when gets jumped by Marcel's spies (yeah snooping after Rebecca in Italy) he beats one without Bex's help.She is impressed and then he reveals his secret she is excited that upon touching him she loses her vampire abilities and feels she can live out her normal human life with him.She invites her sire progeny to have Matt test it out and again all vampires around him or touched by him have human vulnerability.Strangely they become addicted to him especially Rebecca and fall under his control.He returns to MF a very popular guy and it's strange to everyone how he has changed into a cold and bossy guy and he realises it too like he is conflicted he knows he has never been this popular before and vampires are no threat to him anymore and yet he knows the clinginess and dependence of the vampires around him  is unatural plus he realises every time he cures a vampire he gets a rush and yet the power is addictive.He keeps having nightmares of the cured vampires haunting him with a strange appearance and he sees himself acting cruel in his dreams to Rebecca draining the life out of her .When he runs into  the 'angel' he met he wants the power lifted from him but he is told he now belongs to a new race of the succubii/incubii and they are there to keep the balance to immortality.So we introduce a new species in this way.Matt decides he does not want to have Rebecca around him coz she's enslaved to him like a drug addict and it's going to kill her and so in the end they part ways in a heartbreaking way (kinda like Lana and CK is Smallville 9) ..It's high time Matt became a serious player in the show's story that would be cool

Just my thoughts 

I'm hoping Matt stays human but that he finds a reason to get involved in the main plot other than being the human compass would be good for his character.

I like the idea of turning Tyler into an anti-villain because aside from being Caroline's sex bag and basically forced into being Klaus's first successful hybrid he was never much of a character and yes, add another witch that he found. That person doesn't need to be a new main character though, just a recurring one. He needs his own character though so make him independant, like trying to create a pack of hybrids (if he can make them) where he becomes the Alpha male now that Klaus has left.

Katherine going to Caroline for help is the obvious-non-obvious route and I agree with the reasons Lynx81 mentioned.

As for new main characters and new types I'm not sure. New types I'm a little worried about, it's a show mainly about vampires so I think one of the new main characters could be one that Caroline would get along with, preferably a girl so it doesn't become yet another drama triangle. The other(s) could be a new type but I just hope they don't screw up the mythology or the visualization of how they will look and react.

No one has tried it, but if things ever get desparate someone may want to try Tyler's blood as a cure to Wolf poisoning.  Why shouldn't it work?  Second, I really do think that our new witch will be someone we already know, a bit of a surprise if you will.  

I also agree with you Lynx about Matt.  SOMETHING must happen to him this season.  i know it's great having the human on the show...but he isn't a very good one.  So something has to change, this year.  Rebekah will leave as you said, maybe halfway through the year--if they go to Europe there is always the chance that they run into some old nefarious tales of "The Originals" that make her "nostalgic" and leave Matt sick to his stomach that people could do such horrific things.  This may make her finally realize that they really are one world away from each other, though they care for each other...

I'll have to think about some of the others.  I imagine Damon, via Jeremy will safe er' save Stefan; I imagine this will happen five shows in or all the way up to the mid-season finale if Silas (channeling a miraculous Stefan) does a great job...making even Damon like Silas a bit more!

I'll have to think about the rest; I'd guess on Katherine but I TRULY do not know what will happen to her when she wakes up.  It'll be interesting that is for sure.  I also plan to see April back again at some point IF she is also going to college...

I think they left that as a plot device that only Klaus can cure people because he's an Original Hybrid, one of a kind. However, I think it would make sense for Tyler to be able to turn other werewolves into hybrids just like any vampire can do but he'll need a doppelgänger for that which might mean they could go that route with Katherine. I just hope they don't go that route regarding Klaus because I think they should move on from the Klaus-hunting-Katherine story now that Klaus is going to try and settle down and Katherine got her freedom.

I believe that they will move on from the hybrid making of Klaus. He seems to have his hands full with Marcel and his group. With protecting the pregnant wolf gal and trying to reestablish himself as top dog in the big easy.

Fascinating prospect that Tyler could possibly make hybrids himself. I actually like to see another triangle. A good candidate would be April. Matt seems to have the designated human role of the show locked up. It is Mystic Falls, and I suspect April will be revealed to be more then just a ditzy human gal who is the daughter of a pastor that helped eleven others blow them selves up in a gas explosion. Just what if she is a werewolf, and this season she is coming into her first change. With Klaus gone and Kaylee also in New Orleans. It leaves Tyler to mentor her and it be a start to turning her into a hybrid. It be a triangle that is different two gals and one guy instead of two guys pining over one gal.

As for Matt being an Angel or given the powers of an Angel/guardian. I don't see this. I suspect he will be joining the girls in college. Elena and Caroline, I know he doesn't plan on going. That is because of his financial situation. Although that is rectify with Rebekah paying his way for college. Also giving him space so he can decide whether he wants to become a vampire to be her (near) immortal mate. Allowing him time to choose, as she heads to New Orleans to help her brothers.

Back to Tyler and April. With Caroline off to college and Tyler returned to Mystic Falls. The April plot is perfect.

I agree, something has to happen with April.  It would be HORRIBLE to waste the time to introduce us to her and write her out of the show...we'll see.  I agree she also should most likely fill the "werrewolf" niche, as there is absolutely zero, like our witch (but I got ideas for that).

If she "tries" AND succeeds at hybrid, good for her, but that may be a scary prospect...unless she is cool that death is on the line.  But, with Silas out there, maybe that will be enough.