Ratskinner
Adventurer
Because Next could potentially be that "generic" bucket of Legos that can be built into almost anything, will there even be a "default" method of play?
It sounds to me as if there will be a presumed "basic" set of rules. These will be a subset of the "core" which will include a mess of modules designed to emulate feels from various previous editions.
Now, if that "basic" game is also the assumed "default" set of rules, I don't know. TBH, I doubt that even WOTC knows, at this point in the process.