Instead of a Sinnoh remake, why not a remake of Pokémon X&Y? It's already too late for a third version of Gen 6, so a remake is the last chance for the Kalos region to redeem itself. I don't know if Game Freak can make the hypothetical Sinnoh remake as good if not better than Platinum... Here's my wishlist for the hypothetical Kalos remake.

Wishlist for XY remakes:

Megas for the Kalos Starters (I know Greninja has Ash-Greninja, but only a Greninja with Battle Bond can do that and before you ask "Chesnaught and Delphox should get Ash-forms", Ash never used them.) as well as Megas for a few Gen 6 Pokémon
Post-game episode involving Zygarde and a return of Team Flare under the lead of Malva
New sidequest in main plot involving collecting Zygarde Cores and Cells though unlike in SM, they remain active 24 hrs. a day. If you collect them all, you'll get a Zygarde with Power Construct.
Giving both the Gym Leaders and the 3 Friends (Shauna, Trevor and Tierno) more characterization like Gen 5
Rematch of the E4 with new stronger teams, including a Mega for each of them (Diantha gets a different team too, but keeps Gardevoir)
Gym Leader rematches in the Battle Chateau now have a full team, including a Mega
You can now rematch with Shauna, Trevor and Tierno, each with a full team of 6
Battle Maison now has different styles ala Battle Frontier
New areas to explore such as the Power Plant and turning the Chamber of Emptiness into a dungeon. There will be no music playing for the latter as it's going for a "Nothing is Scarier" approach.
You can collect every legendary so far like in ORAS and USUM. You get them through rings like the former. But if you collect every single Legendary, you'll have a battle with Hoopa. If you captured it, you'll get a Prison Bottle
Like in Gen 7 and LGP/LGE, there are no HMs. In fact, you use your Pokémon for HM stuff.
I know that's too much to ask for GF to do, but we can dream. How would you rate it if it's real?