Most players enjoy challenge, hence why we have this thread. Players that enjoy challenge are saying the rest mechanic makes the game too easy, which is largely true. But maybe the correct solution is to simply add additional difficulty levels to the game for players that want more challenge. As it stands now, the rest mechanic is only one feature that makes the game easier, but another includes the infinite use of familiars (especially imp familiar). In its current state, the game is whatever you want it to be.
The limits on the rest system can absolutely feed into the difficulty of the game, and I would love that. The fact remains that at the moment you can make it as easy as dumping all your skills and spell slots and then resting immediately, which is obviously the optimal thing to do if its allowed. It cannot be allowed, and the 5E rules already make that clear. We need to translate that into a mechanic in game which is what this thread is to discuss.
We need to know what the system could be in order to come up with the knob you can turn to increase/decrease its difficulty.