I'm genuinely excited about Sea of Thieves, despite not really being into MP games that much.
I really enjoyed my time with the Division, because it struck a balance which allowed me to do my own thing a lot of the time and rare seem to be pushing this too, with the smaller single person vessels.
Probably more so than the Division though, this game looks like you'll need to actually chat over the mike to do well, which is always a barrier to some. Looking for Clubs will hopefully help in this regard, but there will be some simply unwilling to play that way.
As to the Old Rare/New Rare thing. Rare was always known for innovation and doing something new. It's nostalgia that seems to have linked them more with mascot 3D platformers more than anything else. As much as I think YL will be well received, there's no doubt that Playtonic are lifting wholesale a format from years ago, with little in the way of innovation. I guess as a smaller studio there's less room for risk taking and they have sniffed in the wind a nostalgic desire for this type of game. Fair enough, there's room for everyone.
That said, it's SofT that is continuing the Rare tradition for innovation more strongly than YL.