Matt, all great questions!
To be honest, we are flying by the seat-of-our-pants at this time and don't know how everything will shake out. Will a lot of people purchase Playdate? We hope so, but don't know. Will people love the Season concept? That'd be great, but again, uncertain. With that in mind, let me try to answer your concerns:
- Does talking about my game in public affect my future options for being part of a Season?
No. I would say that releasing your game would probably jeopardize its inclusion: we definitely want new games. But it's okay if the game itself isn't a secret: its inclusion in the Season can be the surprise! (Caveat: we'd like our current Season One devs to keep their games secret.) 
- What is the official path from Developer Preview to being part of a Season?
There is currently no official path, other than making sure that someone at Panic sees your game. We probably will formalize this in the future.
- Will there be more than one Season of games?
We're not certain yet, but I think it's likely. (And even if we don't do "Seasons" in the future, Panic will figure out some avenue for releasing and promoting games it likes.)
We're also actively exploring ways for developers to release and monetize Playdate games that won't involve Panic at all. We'll have more to say about this in the future.
Thanks for your questions!
Greg