This a difficult task and I am not sure there is an "ideal" rest mechanic for D&D since the game incorporates a wide variety of playstyles.
I think an ideal system would recognise the different styles and break out the various resources involved and allow the DM to cycle them on different recovery mechanics.
What do I mean by this?
Essentially at the moment a D&D character has a number of resources that reset on rest breaks. They are; Powers (spell, Ki, maneuvers etc.), inventory (scrolls, potions, etc), and health (hit points, hit dice).
There is not particular reason that powers should be recovered on the same mechanic as health (rests). Powers could be recovered on a clock (At dawn of a new day, with or with out a rest, for instance) where as health would need a rest or a rest in a safe haven.
The DM should be supplied with enough information to be able to set the various recovery mechanics to suit the style of game they want.
I am not sure what those mechanics would look like though.