On the thought of an Endless mode, that is a good point but when getting further into the game and having enemies constantly spawn, there comes a point where bushes and chests feel kind of like a mute point because enemies still drop glyphs and equivalent base boost items or even better items for that matter. But there's still also forced map regeneration which is that failsafe of preventing an empty world state or with things scaling too fast early on for a new game. An example of that was with 0.2.3 (from what I saw initially) where some enemies were able to scale up to their later stages naturally more often, personally seeing a stage 9 bear and goblin on day 3 or 4.
Scaling dungeons is something I thought about where it was based off of time; as days go on, they either get longer, include later stage encounters, or a mix of both while also providing overworld enemies of equal caliber. Like how with enemies scale as days progress, dungeons would scale in a similar fashion with having more late stage enemies with earlier stages being spawned into the Overworld. A good way to put it could be: current enemy scaling would be fine for the Overworld, but having encounters in dungeons would be a few stages above them with the boss being one of the final 3 stages (7-10) by the 5th/6th day.
Though, bringing up the idea of "new" dungeons would be nice, actually. Or at least something akin to a 'boss rush' dungeon where later stage enemies act as normal encounters/elites. Perhaps unlocked as quests go on, with story progression continuing, those rare dungeons could end up becoming more numerous over time.