And that is how it will work in this game too. If you are wearing heavy armor you won't have the regen of a mage who is only wearing light armor. So you are at a disadvantage in being able to fling off as many spells as him, but you trade that off for more survivability though. I expect that with enchanting in this game that you will be able to put enchants that increase mana regen to make heavy armor more appealing to mages, but it still won't be as good as the light armor though.

Opportunity cost, yes. It looks like players are going to have to make a lot of decisions. Where to spend skill points, how to assign H/M/S, and what effects they want to focus on.

One expensive skill, with an extremely long cast time, no less. Even if you dump every point you have into stamina, by the base numbers, at level 50 you'll only be able to pull it off 7-8 times. And enemies won't stay at 40 meter range- you might get 2 of them off if they are really slow, but there are enough charge attacks in the skill trees that once they hit 20-28m range, they are going to be in your face, or using their own ranged attacks.

In PvE, it is an initiator, and little more. In PvP it will be useful for smacking people that aren't paying attention, but in a real fight, the cast time is an immense burden.