As you pointed out, there's the sustain issue, you will lose a lot more resources, a lot faster. Also, you lose about 5k stam/magicka (that's what I'm losing, at least, it depends on how many CP do you have) from the champion points, and some critical rating, which you don't invest in anyways, so no problem there. Now they removed the cost reduction passives, that's not an issue anymore, but there's still the matter of stam/mag regen you're going to lose, plus the tenacity bonus. That is kind of harsh, heavy attacks restore a lot less resources, but they become necessary.
Survival becomes a lot harder and you really want to plan what set to use to make sure you don't get instagibbed.
Not sure about BGs, there's probably going to be a whole different set of mechanics, but as for the no CP campaign, you really want heavy armor, unless you're a shield stacking sorc or a nb.
Basically, you're playing a level 50 toon with cp160 armor, that's it. The builds you're going to be using are much different, and the gear as well.
Hope this helped