As long as they're heavily time/resource gated and there's much fewer oGCD heals, DPS neutral GCD heals don't have to be a problem. The main benefit I think they'd bring in comparison to oGCD healing is the fact they slightly break the 111 monotony if done right. They become bad when they're always readily available and have no risk to use, this is the problem that the current healing paradigm has with its glut of oGCD heals where we can ignore the base GCD heals because they're just not needed most of the time.

Ideally healing should have some cost associated with it rather than being always neutral. If you want top DPS as a healer, then you need to also have the most efficient healing, not just simply having healing available, top DPS as a healer should be a highly risky venture as you're ultimately playing with everyone's life. The cost doesn't have to be much, a "loss" of about 100-150 potency per resource (GCD/Stack of whatever/Gauge/MP) similar to Energy Drain.

Out-of-combat prepping I don't think is a bad thing either; a lot of jobs generate some resources outside of combat, cooldowns themselves are something that generate outside combat, so using some healing reserves to charge an attack isn't necessarily bad, but mob damage should be increased so that it's riskier to do so. Worst case scenario Square could always slap a "while in combat" condition to the heals to not generate those resources.