Yeah I don't think Obsidian is out to make [censored] DLC which feels like a modded add-on and nothing more. In terms of actual size though, I think one thing we need to keep in mind is that pure map size means nothing. If it is a huge map half the size of the Mojave, but with nothing but repeated textures and copied and pasted terrain with generic enemies populating the area, that would be incredibly disappointing despite the "size". But if it is an open wide area of even 1/6th of the Mojave, but is packed with unique content and good area design mixed with optional events and quest hooks, that would be very substantial and interesting.
Well based on DM I doubt we'd getjust a small area copied multiple times just to make the dlc bigger it just doesn't seem like they'd just phone it in, I think we'll be looking at pretty much everything being new and not just transplanted from the mojave. I"m wondering how much is going to be wide open versus the winding canyons it seems like gameplay wise they'd be able to do some new things with it like enemies attacking from above or trying to force you into a dead end so you'd have to fight your way out, it seems like the canyons would make great ambush or hit and run areas, and I think we'll see a fair share of locations caves and tribal camps seem likely and the trailers shows what looks like an old park ranger post so a few areas like thay would seem appropriate, then theres the question of where all those 1911's came from it seems like a large weapon cache or a few small ones were scattered in Zion so it would make sensd for them to come from nearby it would also explain the SLCPD vest Graham has.