I saw this supposed "leak" the day before of Gladion as the President of Aether Foundation and now this supposed "leak" is looking more realistic, but I don't know until more details are released or I play the game.
The DS remake is still playable on the 3DS and the Pokemon from them are still transferable to the current Gen. With Gold and Silver coming to the system, all six of the previous gens will be compatible with the current games in some form. It'd be weird if 2nd gen was left out.
I'm guessing Crystal is coming out at a later date because otherwise everyone would pick it over Gold and Silver if it came out at the same time due to being overall better in every area, unlike yellow which doesn't nearly have enough advantages over Red/Green/Blue to always be chosen over the others. Also the in-game coding for both Pokemon bank and 7th Gen have 7 game-origin identifiers that use the little Gameboy Symbol on the Pokemon's status screen, currently four are being used (for Pokemon from Red, Green, Blue, and Yellow), and now two more are being used up(One for Gold and one for Silver), so Crystal is inevitable.
And just in case anyone is curious, there were also 2 unused game identifiers for 7th gen games(As in using the alola flower on the status screen), so USUM are probably the last 7th gen games. Also Pokemon Go has a game origin identifier complete with unique status symbol for Pokemon from the game(a "G" surrounded by a circle)
I really hope that Ultra Sun and Ultra Moon will be sequels like Black 2 and White 2 were. There are a lot of plot threads from Sun and Moon that can be expanded on: Lillie's Pokemon journey, how Alola has changed now that is has a Pokemon League and the Battle Tree, the Ultra Beasts, etc. Actually, just the "Ultra" prefix indicates that the Ultra Beasts will probably be playing a bigger role this time around.
I'm also just hoping that the new games will fix some of Sun and Moon's gameplay issues (like how fucking difficult it is to level up Pokemon once you've finished the main story).
Finally happy they're getting around to porting over Pokken to the Switch. Moreso that they are finally including the Arcade content and more in the game now.