That's the one thing I am worried about. It would bloody well break my heart to have to boycott this game over spurious DRM. Personally I am of the opinion that no DRM is necessary at all, but then that probably makes me look like an extremist
I suppose it will depend on who the publisher is in the UK/US etc., which isn't known yet (only that 1C will publish it in Russia), and hence what that publisher demands.
As far as I'm aware the B17 was never a "flyable" plane in IL-2 but that wasn't because of game engine limitations limiting the number of engines-per-aircraft or anything like that. Though IL-2 certainly does have its share of built-in flaws of course (such as high-altitude flight modelling in general).
Lancasters aren't due to be in the original release of the game, but I think it's inevitable that they will be added eventually in one of the many free patches or paid-for expansions we will see over the years. What's going to be nice about BoB is that, in theory, this time around the engine is being made flexibly enough to be able to "properly" incorporate every feature it might later want to add (such as radar, jets, whatever).
Estimated list of flyable and AI-only aircraft in BoB at release (among other details)