While I agree with the sentiment, I don't think any of those options is viable, for a couple of reasons:
1) Proc heals are unreliable, especially on such long cooldowns. This is especially true for sages and scoundrels as they will always have multiple heals going on on multiple targets. Less so for commandos but still likely not worth taking. Even boosting the proc heal would be pointless as it would boost it to a random target and, at the same time, would benefit way too much shadow tanks (for whom the relic is amazing)
2) A plain power boost would likely make the relic extremely valuable for DPS and would probably conflict with PVP as well (since there would be no way to "block" that relic in a PVP environment, and being scaled to 72, or 75, or even higher item levels, it would quickly surpass the power boosts from PVP proc relics).
I think the best option is to do something like this:
- Leave Ephemeral Mending alone. Its usefulness for shadow/assassin tanks shouldn't be touched.
- Add a new proc power relic, "Resplendent resurgence" or something like that, which stacks with serendipitous assault BUT procs only from healing AND, like triage adrenals, reduces outgoing damage by some 20%. So it cannot be abused by DPS and it cannot be abused by shadow/sin tanks in dps gear to achieve enormous power boosts.
This would allow healer to safely have two power boosts, for similar amounts as what was possible before, while not giving dps a new option and without messing with the existing shadow/sin balance.
[Edit: a simpler option would be to just give a boost to healing power rather than raw power, but I'm not sure THAT can be done, while the adrenal mechanic already exists]