I kinda forgot about Adventure Mode (I know they really want to implement it but at this point I don't think it'll be here until 2033), and I think that you're correct. It's honestly a shame that they chose to withold, instead of going ahead and releasing tidbits anyways. I guess part of it is that I'm not bothered by spoilers, so knowing AM content before it's released would not at all bug me, if anything I'd get more excited while playing because "Oh I Know About That!" but that's really just me being a dweeb.