We are indeed experimenting with a reduction of AP-on-Crit.

At the moment the default AP regen is 10/s. A standard AP-On-Crit loadout increases this easily to 22 or more and it was definitely heading into the territory of spamming expensive spenders non-stop right out of the gate. Reaching that point should be a state you aspire to and work towards (usually with some legendary items or a sweet set bonus) - not something that's handed out virtually for free.

It completely negates the use of Signature spells, and we do strive for a rhythm of alternating between your left and right mouse buttons, as well as all 6 skills on your bar. It's okay if the most dedicated players reach a point where they no longer need a signature spell, but this should not be the case for people who just put on 2 easily-acquired items and a particular skill loadout.

Yes - we are pushing for people to do more than spam one skill. Running out of resource should be a very real concern - that's the point of having a resource system at all. You decide when to spend your resource. Sometimes you save it up, sometimes you spend it liberally. If you never run out of resource, what is the difference between a cheap spell on an expensive spell? In theory, a high resource cost spell should do more damage but you can't use it as much. A low resource cost spell you can use more often but does less damage. What we were seeing on both the Witch Doctor and the Wizard is that people simply spam their most expensive spell possible and hope the monsters are dead before you run out of resource.

The Barbarian had reduction to resource regeneration from passives as well. We'll continue to monitor the Witch Doctor, the Wizard and the Barbarian. We're concerned both with making sure all 6 classes have good power levels relative to one another, and we're also concerned that all 6 classes have a variety of fun playstyles available to them.

Quick follow-up for clarity. We intentionally did not modify any legacy items. We have a core value on the team to take great lengths not to modify items on the live game that people own. The reduction of AP-on-Crit applies to items dropped in Loot 2.0 only.