Like, Mega-Charmeleon? It is very unlikely. NFE Pokemon has no reasons to get Mega-Evolutions, except for Pikachu and the likes.
However, it is confirmed that some Pokemon that aren't fully evolved three stage lines, such as Mawile, do get Mega Evolutions. So Pokemon without evolutions or weak Pokemon could get a Mega-Evolution, like Mega-Wormadam, Mega-Drifblim, Mega-Alomomola ...
A certitude is that Pokemon proper to Gen VI (e.g. Talonflame) won't get any Mega-Evolution.
Hope I helped ;)