I've been thinking about this for a bit. My wife and I really enjoyed playing Let's Go together, so I hope they continue this subseries. 

But what about mascots for each generation? Should there be 2 new mascots for each generation? I personally think they should just keep Pikachu and Evee through the whole subseries for a couple reasons: it would feel like you would be taking the same mascot Pokemon with you throughout all of your adventures; I honestly don't think that they can come up with 2 Pokemon who feel like or have earned the mascot status. Yes I know, everybody has there favourites, but Pikachu is an obvious one, while I feel Evee was kind of forced at first... 

I dunno.... Personally I would take Pokemon Let's Go (Insert region here): Pikachu or Evee for each one. 
What do you think?

Let's Go Johto will have marril and togepi. Those seem plausible enough.

Though if I had any choice in the matter I'd rather

I thought the Lets Go games were a nice fresh take on what is otherwise a very repetitive, poorly paced/grindy, and formulaic series. I'm a huge RPG fan, but Pokemon always felt like, "you played one game, you played them all." And, while that would be fine, it was the huge amount of grinding and such that bothered me, every game after the first one I played had a "Not this shit again" feeling. I think Pokemon Let's Go finally beat that by making XP gaining more varied and entertaining.

Id bet Pichu and Togepi
I think togepi is as popular as eevee, if not more.
And pichu can get some of pikachu popularity

I hope they just give up Let's Go franchise altogether

Really afraid of 4th gen remake end being another Let's Go game

Maybe Let's Go was a one off to buy more time for Sw/Sh development??

Just make it one game and call it the region (I.e. Let’s Go Johto!). But GF won’t do that because they’re too greedy.