Speaking of other mechanics to impose a time constraint and therefore limited rests. The game Desktop Dungeons uses fog of war as a healing mechanic. As the character explores the map, they regain hitpoints. Such that the timing of exploration vs combat becomes strategic and integral to success.
How about using fog of war and filling in the blank areas on the map as a way to simulate the passing of day into night. And allow characters to rest peacefully once night time has fallen. If the party is desperate for rest, they can carefully explore while avoiding combat until they trigger a rest.
Would prob have to combine this mechanic with others mentioned to account for when the entire available map has been explored.
