Yeah, now they actually have the ability to do so I really don't see why they won't do it other than for marketing purposes. It's seriously annoying though, because battles will be hugely restricted since a ton of people will use the new megas with their epic stats and such.
you now NEED a copy of OR/AS if you want to enjoy the new megas or play in the updated metagame.
sucks for people who don't even like Hoenn
They could do a patch, but that doesn't make them money.