Sadly, there is a probability that we won't get new megas and if they do they would be ORAS exclusive.
Yes, I know what you're thinking, Nintendo can patch the game, but it wouldn't be that easy.
First, background information, when you patch the game, you can delete the patch from the SD card and play the game unpatched, v1.0 again. The only things patched so far is the network protocol and the routine to check for glitches in Luminose city when you could get stuck.
If they ever patch the current games, they would account the possibility about deleting the patch and reverting to 1.0 after new things were added, and in that case new data in the save would've unrecognized by the 1.0 version.
So, with pokemon project and smealum confirming that there isn't more placeholder information or items availables, Nintendo could just added new mega forms that would work in ORAS (like the Deoxys form from FRLGE) wich would work only from those games but compatible when battling with x/y.
But having those like that would've too unreasonable.

What do you think /vp/?