Armaldo - OH WAIT, I TOTALLY FORGOT HE EVEN EXIST. Yeah, that's pretty much your reaction right now. It's a half decent wall, so I'd like to see a Mega evolution of him in the near future, Gamefreak probably forgot about him anyways.
Floatzel - Despite being one of my favourites I never really used him competitively so I don't know if he really needs it. But It would be cool if he gets one.
Zoroark - It's one speedy son of a penguin, give him a Mega for no reason at all.
Arcanine - Days long gone and forgotten and so gets the Pokémon that used to be on your team back in the day, even to this day he is still awesome and useful if used right, some what, even when he gets slowly little by little less productive, Giving him a Mega would be a fresh start of his return.
Pidgeot - After third generation he totally kicked the bucket on my point of view, give him a Mega Evolution.
First generation Eevee Evolutions - Why? Did you even need to ask?
Luxray - If he needs one or not is irrevelant. Give him one, because he also need super saiyan hair.
Ninjask - I always felt like he may have potential wether that he develops that, is both yes and no, giving him a Mega evolution could be quite interesting.