In regards to the discussion on being the last game therefore Red should be there... I agree with Hikari. After the whole deal regarding Pokemon 20 and the Superbowl ad I really doubt they'll head that route. Given how much money one Superbowl ad would cost, why make this the last game and still buy a super expensive Superbowl ad? Why not keep the money and run, y'know? I just can't think of any reasons that indicate towards it being the last game other than the celebrations of Pokemon starting.
I mean last main-series game maybe - the rest could be remakes of the past, or alternate worlds based on them. Ending at 800-something Pokemon is fine I suppose, we do have a lot after all, so yeah, it isn't completely out of the woods. It's just really unlikely considering what they've campaigned with thus far this year.
Red is most likely to appear because of the anniversary of the original games. If it wasn't the anniversary (and RBY wasn't recently re-released) then I don't think Red would even be thought of as reappearing. Cynthia would be more likely. She's more recent. She appeared in Unova and she certainly made more of an impact than Dianthia, Alder or Iris. She'd appeal to the current generations more. Red as a non-playable NPC doesn't really appeal to anyone other than those who grew up with the games. It just depends whether they're aiming this towards the newer generation of fans or older generations. From the looks of it, there could be a balance of both, so Red could definitely appear. It's just not guaranteed.