I've been reading alt.tv.twin-peaks.com archives lately, reading people's wild WKLP theories and other speculations and reactions, and was thinking, pity I'll never have a chance to take part in experiencing this type of thing firsthand. Well, who knew.
So to put myself on the line and gleefully risk looking as ridiculous as some of them (love all the Andy-did-it theories that popped up)...
1) I'm leaning toward the miniseries idea that JerryHorne mentioned as a rumor. I really don't see an ongoing series but rather a limited-run show with the possiblity of future entries if popularity warrants and inspiration strikes. That's the way prestige television is trending anyway.
2) I feel 100% certain that this is major news and not something other than a film or series in the works (a novel wouldn't involve Lynch and anything other than TV/movie would feel like a let-down after these expectations). They knew what the reaction would be when they did this. Despite all the CW to the contrary, Lynch isn't really a tease. He pretty much always follows through on hints and suggestions, though the answers may not be what we expect or be easy to crack. He delivers. Same goes for Frost. These are the guys who had the killer pegged back when they thought the show would perpetually delay his reveal - well, at least if they are to be believed ;).
3) There will be another mystery, but I don't think it will be too similar to Laura's murder. Maybe not a murder mystery at all. That would feel too much like a repeat and I think they want to avoid a sense of retreading their steps as much as possible. I wonder if the mystery will be more overtly metaphysical/mystical this time - a general sense of unease and dread without the specific hook of a dead body to pin it too. I just said on another thread, on another site, that Twin Peaks needs a strong narrative hook to thrive. But while I do think the storyline will be important to the new series (it won't be purely an exercise in style and mood) I could see it being something more diffuse than in the original.
4) That said, Mark Frost's involvement will ensure a more disciplined narrative approach than Lynch's recent films. This will probably be his most straightforward narrative since The Straight Story though there will be enough room for detours that will make Inland Empire look like a Disneyland ride. It will be really fascinating to see how the two collaborate in 2015(ish). Their sensibilities have grown much more divergent since 1989 yet obviously they wouldn't be launching this project if they hadn't already tested the waters to see where they coincide or can give each other space to do their things. I don't think we'll be seeing guest directors or writers this time around. It will be Lynch/Frost all the way.
5) It will be a hell of a lot more offbeat and weird than the original series. This isn't just a matter of raising the stakes but an inevitable byproduct of where Lynch is at in his career. From Fire Walk With Me on, he has grown wilder and wilder in both style and narrative approach. The conventions Twin Peaks is bouncing off have also become more out-there at this point. I have a feeling the new Twin Peaks will have fewer light elements - both visually and tonally. I think, visually, it will be more abrasive too: probably shot on video (at this point I don't think they even make PD150s anymore, do they? so it won't look like Inland Empire which many will find a relief, though personally I like that look) and the surreal Lodge sequences will be more akin to the Missing Pieces than the original Red Room stuff.
6) I think they'll mostly avoid the nostalgia trip aspect by limiting familiar faces to smaller roles (though as noted above, I definitely expect Sheryl Lee to return in some important capacity - and for the character or name of Laura Palmer to be evoked at some point, since she's always been central to Twin Peaks for Lynch; they will have to feature Kyle MacLachlan centrally if not extensively - i.e. he'll have to be an object of investigation or a haunting presence if not a main character; and even if he only appears at one point, Ray Wise will have to be in it and will have to be a huge part of whatever episode/sequence he appears in to the point that we'll remember the part as being bigger than it was). Perverse as it may seem, I kinda suspect it will not be set directly in Twin Peaks but nearby (not Deer Meadow either). I'm probably - most likely, even - wrong about that, yet it's a lingering suspicion.
7) The Black Lodge will feature HEAVILY in the show to the point of consuming an entire episode or two. Lynch just loves that world and it will give him an excuse to pull out all the stops and just get as crazy as possible within the confines of a major miniseries (and yes, even today for all the patting on the back TV people do, they still have confines). Perhaps even more importantly, it gives Lynch an excuse to feature Cooper and the Palmers heavily. He will certainly be keeping his "Between Two Worlds" word to Lee, Wise, and Zabriskie (whom I also think will get an important role in the story, more important probably than she had on the original show).
8) Bob will not be recast. He = Frank Silva, now and forever. I think Lynch has too much respect for the source of his inspiration to pull a Moira Kelly in this particular case. Silva's image spawned the entire shadow world of the series and he cannot be replaced. There are plenty of other Lodge creatures to play with and I'm sure he can figure out a way to convey Cooper/Bob without showing Bob (or somehow incorporating old footage). I really hope they bring the Jumping Man back. I think he may be the Lodge creature who terrifies me most.
9) All predictions about David Lynch will miss the mark in one way or another. That's why we love him. :)