On the point of Endless Mode (or Infinite Days) the issue is Bushes, Chest and mainly Dungeons do not re-spawn (currently) and this ultimately will lead to an empty world state
The idea of scaling Dungeons is something I think would be interesting, the problem is how the scale (deaths/surrenders, or time) and the effect on game progress (take to long to find the Goblin Village and it is too strong meaning you need to world reset), however, I see the possibility of new Dungeons being added as Quest are taken and completed, expanding the world that way
This then brings out a new problem...you can't explore the current map size in a single day, so rare locations may not be found just due to searching in the wrong areas (the warps help, but it isn't enough at the moment)