ORAS isn't a remake of Emerald. It's R/S. or you could say it's a remake of all three (it isn't). they even registered the trademark "Delta Emerald". ORAS has a lot of variety from RS, but it's still much different from emerald. No battle frontier (or even battle tower for that matter, being replaced with the battle resort), the champion is steven, not wallace. and many other differences.
Omega Ruby is Ruby redone with a fresh story, new characters, altered maps, and of course, mega evolution. While Rayquaza is featured in the game, and is indeed catchable, it is not because of events dealing with Groudon & Kyogre in emerald, but added events from neither emerald nor ruby.
OR has groudon
AS has Kyogre
An emerald remake would have both.