I know everyone thinks "they don't do third versions when remaking", but I don't think we know remotely enough to draw such conclusions. And the little we DO know, is not as expected.
I'm not saying that Delta Emerald is a realistic possibility because of them registering this trademark, in fact this is as meaningless as any other trademarks they've been registering.
But there is 2 other things that prevent me from drawing the "not gonna happen" conclusion:
-firstly, gen 3 is when the "third version" only really became notably different to the point where you cannot just "put the Emerald stuff into RS". With HGSS, they could easily put Suicunes side-plot in it with no problem, but its impossible to just add Rayquazas act in RS and keep the focus on the cover mascot at the same time and/or not involve the other mascot. in the Hoenn games, they planned to have the complete story in the third game and hence told a simpler 1 legend story in RS....so unless gamefreak is fine with the simple version for the remakes and not involving Rayquazas part whatsoever, this is an issue that cannot be addressed without a third game. They might be fine with the simpler versions and a bored Rayquaza in the post-game though, but Id think they wouldn't leave it incomplete like that.
-secondly, the legends on the covers have different appearances, which are pretty much guaranteed to be new formes. And that means that the plot will deviate at least to some degree from the originals. If these aren't copy&paste remakes, then we don't know what we're in for, and it may be a changed plot that makes a third game more unnecessary than it already is, or...it could set up for one in a way we aren't expecting that would actually justify another Hoenn game.
Add to that how gamefreak do what they feel like at any point, rather than following some pattern that never holds up...and not to mention the option that BW2 showcased, an "Emerald" likely wouldn't even be just a third version but a sequel to these remakes, with a later plot, locations and features of its own...if it was made that is.
So I wouldn't rule out the possibility as quickly as I usually would, but I'm still expecting ORAS to be standalone Hoenn-business, and a return to Kalos part 2 to follow after them.
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Now for some pointless crazy speculation LOL.
If ORAS featured a modified "Mega evolution"-concept in the form of Alpha and Omega evolutions...let me recap those first:
Imagine if particular Pokémon could Alpha-evolve and Omega-evolve in the respective game after obtaining the Alpha/Omega Orb or whatever the key item would be.
Instead of turning into overdesigned (Mega) versions and having their base stats boosted by 100, an Alpha/Omega evolution would cause a weather change (as consequence of the evolution, NOT from an ability change) and a less significant stat boost of say 50.
So for example Alpha Kingdra and Alpha Ludicolo would unleash rain, while keeping their abilities to abuse it.
Same for Omega Shiftry.
But not just with sun and rain. Omega Flygon would cause a sandstorm, and Alpha Walrein hail.
...anyhow. If there was a sequel at a later time in the form of Delta Emerald. It would obviously come with its own set of pseudo-evolutions, Delta evolutions.
Since RS do the weather theme, Delta evolutions would have some other focus.
Delta implies change.
So the focus could for example (and any TCG veteran would come up with this right away) changing a Pokemons type. And not to something expected like Charizard finally becoming a Dragon, but adding elements that you wouldn't see coming so easily, along with the respective ability to change Normal type moves (Pixilate/Refrigerate/etc)
Delta Linoone turning into an Electric type, Delta Salamence into a Dragon/Steel type or something..
not to mention then there'd be one for each golem:
Alpha Regice
Omega Regirock
Delta Registeel
of course none of this is gonna happen lol