Thinking about season 3, folks. And the more I ponder it, the more I am utterly befuddled by the idea that season 2 is a bridge season.
Because if someone says "Yeah, we had a sequel planned for the book- but we need a bridge season to get to that starting place for the series." You anticipate that the setup for the sequel was all in the book, but some crucial bits of that setup were cut for TV. You think, ok, so this bridge season- season 2- will mostly be highlighting things that were in the book which were cut from season 1, combined with things that might have ended up in the prologue of book 2, with some fun extra bits for the sake of a coherent narrative.
There was a lot of "fun extra bits," but for the most part? That's. Not what season 2 was.
Season two was a lot of things- I like to describe it as a love letter, to the fandom, to Terry, to all the people involved in making the show- but it's hardly any of the things I listed above. There's some touching on book-things left out of the show, I can't think of any good examples now, but a lot of it is new!
And those new things made waves, that's absolutely sure! Season 3 will start from a very different place than season 1 ended. Aziraphale's in heaven. Crowley's a mess. Gabriel and Beelzebub are a thing. Muriel's running the bookshop.
But none of those could POSSIBLY have been crucial for season 3 to work.
It would have been pretty wild for 668: The Neighbor of the Beast (the proposed title of the book sequel) to have begun with Aziraphale suddenly in the position of Supreme Archangel. Even if they had a little explanation in the early chapters, it would have been weird- in the first book, there's very little in terms of heavenly politics. It would've been equally weird to have Crowley a mess over their off-page breakup. If that was why season 2 was necessary, Book Omens would've needed a bridge too!
Additionally, from what we know of the planned book, Crowley and Aziraphale were originally planned to work together- I lost the post where this was summarized so long ago, but I vaguely remember mention of them road-tripping across America, which will have to be changed now.
So their whole fight- the consequences of the final fifteen? We can assume that was all Gaiman.
Gabriel was practically a footnote in the book, so it would be wild for his and Beelzebub's absence to be fundamental to season 3- and we know Neil got the idea to canonize ineffable bureaucracy after season 1 was put out.
Maggie and Nina were involved because Neil wanted Maggie and Nina on the set (he's said that too). (I could find sources for all of these things if I went looking, but I'm very tired right now.)
Muriel morphed out of a character Neil said was originally Aziraphale's replacement on Earth, but who he made nice because he was sick of writing about mean angels- so, Muriel could be fulfilling a season 3 role set up for that heaven's-replacement character he mentioned- but they probably weren't at the center of the plot, if Neil and Terry had left the character mostly unplanned.
The flashbacks are either follow-ups to flashbacks introduced in season 1 (1941, for instance), unlikely to be relevant (the Resurrectionists) or very unlikely to contain key plot details (the Job minisode, which was written by John Finnemore without much input from Neil at all).
So what was introduced in Season 2 that makes a transition from book-sequel to show-sequel smoother? Dear Reader, I have no idea. I am not a particularly good theorist, just someone who is pretty sure none of these words [this season] was in the bible [original book].
I just keep coming back to the thought that if the start of season 3 was also the planned start of 668 (and we know it won't be), they would've written a trilogy. Because they would have needed a bridge there, too.
I don't doubt that season 2 was necessary to bridge the gap- and I love it, even if it wasn't necessary, I love it and if Neil wants it back he can pry it from my cold dead hands- I'm sure it was, in some way that we have no way of understanding yet. It must all be in his authorial, ineffable plan, because that's where I am with this, I GUESS. But when he says this was a bridge season to something he and Terry had planned out before season 1 ever aired, I'm clueless.