I think per encounter can work. One of the problems with past and even the current edition of the game is the character who uses a limited resource (spells or psionic points) for example, and cannot recover them. The extreme example of this was a 1st level wizard in 1st Edition who cast a sleep spell, and then tried to keep from getting killed as he was generally useless unless he had a bunch of different languages. The effect of this is to limit the fun of the player whose character has limited resources.
Possibly, there might be a mix of always usable abilities by characters (some spells, combat maneveurs) that are always usable in an encounter, and some more powerful resources that have a limit per day.
The key thing is to avoid the "fifth wheel" feeling that can happen with limited resources. (I presume all classes will have things that they can always draw on, such as maybe a basic combat maneveur for a fighter, some magical ability for the mage and clerics, or maybe a maneveur a rogue can always do.) As for power sources, it does seem that there is an emphasis on putting more power in the character, as opposed to items. So, possibly what best defines a character is not the equipment, but the character's abilities and personality.
So far, I like what I am seeing, but I want to know more.
Ruin Explorer, it is good to have you back here!! Maybe we will see a few more board veterans swing by in the next few months as we approach 4th Edition.'s release.