Pokémon Omega Ruby and Pokémon Alpha Sapphire announced

I wouldn't try fitting a timeline to pokemon. The R/S/E games are supposed to take place at around the same time as Red and Blue, so this would be retconned to the place where mega evolution is discovered.

I don't think the remakes can really be considered as canon, persay. That would mean such things as Gold and Crystal Ethan and Lyla going back in time and becoming the ones who are responsible for Giovanni not answering Rocket's call are perfectly sound ( All the while being the ones thwarting them at the Radio Tower at the same time, no less.)

It's easier to consider remakes filler content than retcons, imo.