This is just speculation BTW.
As far as I'm aware, your speculation is dead on.
No matter how many DLCs stand between us and 'full' Adventure Mode, you'll get them all if you KickStartered AM (at the proper tiers) or buy the
"season pass". So far we're getting at least 2 DLCs, with the PvE mode that's coming out next year as the first, and then "Adventure Mode".
There are no plans for a subscription model and the game will never be pay-to-win.