I want to know if Brilliant Diamond/Shining Pearl (I think that was it, right?) will be able to trade in some way with Sw/Sh. I want the Sinnoh mons in Galar! I'm guessing you will be able to send Arceus from Legends over to D/P at the very least. I don't know if we will be able to send Sw/Sh mons that weren't in Gen IV originally over, but it would make sense to allow cross trade with the rest. I think the fact that Gen IV was the only generation with no mythicals in Sw/Sh, and the odd absence of the Gen IV fossils suggests that there will be some kind of trading.
I'm pretty excited for both of these. The D/P graphics didn't look great, but YT streams tend to make everything look a bit worse and they still have until the end of the year (prob November) to make it a little better. Legends looks pretty good graphically. I'm interested to know more about the battle system, since the leaks said it used an ATB system (think Final Fantasy VII, X-2, etc) to some degree.
It'll be interesting to see what aspects of these games they use in Gen 9. I don't see them getting rid of the regular battle system in the mainline games since that would basically end VGC, but maybe Legends could be a new spin-off series like Let's Go. I wouldn't mind Gen 9 having a bit more of an open world element.