I would not mind an option to "turn off Incarnate XP" as an opt out. I have several toons that I never pictured them as being "incarnate" level heroes.
I also would be all for account level discounts for Incarnate XP and such. Basically, the first time you level any character in the incarnate system to +3, all other characters on the account from then on get an x% discount on xp/crafting etc.
STO has a system like this for their reputation system. Essentially, you need to slog through the rep to final tier once, then the rest of your characters get a discount. Really helps alleviate the grind.