I wouldn't put it past him as he blames Matt for Elena becoming vampire as he would have let him due instead. He wanted to kill him before.
He has killed him in last episodes, with his ring on though but still he might if he pushes the wrong buttons. Or if it is a choice to kill him or hurt Elena or Stefan then it would be no issue for him to do it.
(edited by TanithRea)
i wouldnt really be surprised. Its just like him to go and kill the people elena loves or anyone, if he get upset.
With dries and plec saying there will be a love story for Matt in season 6 then I'm guessing it was just a random rumour that Damon would kill him although he might still maim him but the ring would bring him back. Lol also Damon seems to be restraining his natural impulse to kill when upset as he hasn't killed anyone out of his own grief in like a good number of episodes lol.