@sharlatan: "The onlly resource which makes any sence is energy. You get to spend it a constant rate, you can burst it down, but have to pay a price of energy starvation for higher performance for short periods. You can pool it if you know you need it soon so you lay off a bit to save for incomming burst."

So...mana? You get to spend it however you want, but you go OOM if you spend it all in a burst? You can conserve mana if you need to save it for incoming burst?

@DarkWalker: "Active resource systems are not really desirable for Healers because healers are too reactive. While they are not as reactive as in WotLK days, they still have to react quickly to things the boss do on a very constant basis. The added delay of actively generating resource X to be able to use heal Y would drastically change the game for healers."

There is a system that mirrors this in concept at the moment - look at Shamans with Telluric Currents. There are schools of thought that Shamans should essentially forge everything out of spirit into crit, spec into 3/3 Elemental Precision, and rely almost completely on Telluric Currents for meaningful resource generation. Encounter design suffers a bit in this regard, as this build isn't particularly good or not really viable on fights such as Baleroc. But certainly it's not impossible and TC gives us insight on how it works and how it would play.