My guess: Rebekah will want revenge on Klaus after he daggered her for the umpteenth time. She won't want him dead, obviously. But she'll want him to suffer, which is why she'll decide to get to the cure before Klaus and destroy it so he can't create hybrids anymore and will forever be alone. She calls Kol for help, and not Elijah - who would probably want to put a stop to it because it's wrong. She'll also try to strike up an alliance with Tyler because Klaus killed his mom AND his pack and now he's hungry for revenge.
Caroline will be appalled by Klaus's actions and he, in turn, will recognize her as a distraction because it was while he was out flirting with Caroline that his hybrids were staging a revolution against him. He'll also feel betrayed by her and Stefan because they were finally starting to be potential* friends. The Klaroline ship will tread on rocky waters.
The new mayor, Bonnie's dad, will not be so cooperative (like Carol was) with the whole vampire business and he'll resent that his daughter is stark in the middle of it. He'll try to keep Bonnie away from her all-supernatural friends, and she'll rebel against that.
Elena will probably be pissed at Caroline for telling Stefan about her and Damon when she'd asked her not to. Caroline, in turn, will be pissed at her for lying to her unofficial new best friend, Stefan.
I think The Cure is not at all what the show wants us to think, just like with the Sun and the Moon Curse. Maybe it's not a cure for vampirism at all, but a cure for Death. Could it be that Silas created the Cure to bring back his lover whom Ketsia killed? Perhaps Shane is after it to bring back his dead son and wife. He also said that Pastor Young seeked supernatural assistance from him after the death of April's mom. Maybe the Pastor wanted to bring her back from the dead, and so the two formed an alliance, which would also explain how Shane convinced the Pastor to blow up 12 Council Members, including himself.
Which brings us to the second part of the Cure puzzle: the Sacrifice. Til now, we've got 12 humans and 12 hybrids. Is it going to be 12 vampires next? Could Shane possibly have hypnotized Jeremy to obey him, thus enabling him to use Jer to kill 12 vampires as sacrifice? This would also lead to the completion of the Hunter's Mark which is the spell Shane said would raise Silas.
In the preview, Klaus said, "You are trying to grow Jeremy's tattoo. That's a pity." What if he's saying it to Shane? Maybe Shane told him that he knows the location of the Cure, and that he's waiting for the tattoo to grow - which Klaus thinks is a pity because they'll need the sword, which is under his possession, to read the Mark. I guess it's just leverage to make sure they won't double cross him later on.
Now that his hybrids are dead, Klaus must be more impatient than ever to make Elena human again so he can replace those he killed. He might try to take charge of completing Jeremy's tattoo, and his ways often require killing innocents, which could be why Jeremy is so adamant for Damon to tell Klaus that they are 'not going to do this his way.' Maybe Klaus wanted to turn people into vampires for Jeremy to kill?
As for the scene where Professor Shane is being drowned, it could be Klaus' way of getting information out of him. Or perhaps Kol and Rebekah found out the crucial role he plays in the search for the Cure and try to kill him to thwart Klaus' plans/ get information. Or maybe Damon just sees through his lying facade and tries to get him to fess up.
I have no clue what's going to go down with Stefan and Elena, though. Obviously, he's mad and he feels betrayed. He knows that technically, he was the one to finally say that they break up - but it's not like there was any other option for the two of them. He also knows that technically, Elena was under the influence of the sire bond - but Damon should've known better than to jump into bed with his brother's ex-girlfriend a day after they broke up.
This is not me hating on Delena. I know he waited for years to get together with Elena and he didn't want to hold back when it finally happened, but didn't he find it odd that it was so easy for Elena to move on? If he knows Elena better than anyone like he claims to, he should've known that, her feelings for Stefan aside, Elena would also have to factor in her best friends' and her brother's feelings toward Damon. Damon had tried to kill each one of them, and he might've succeeded if it wasn't for Stefan or the ring's interference. He should've known that Elena, as much as she may love him, would want to take things slow.
So, yeah. Stefan's outburst is completely justified. I'm just afraid how Elena will respond to it. I know he'll not turn into his Ripper self - he's stronger than that. It's his relationship with Damon we should be worried about. Because this is the very thing that drove them apart all those years ago.