That seems a totally solid plan. I'm in.
A follow-up note and a question:
[Note] While it might not seem, then, that anything else needs an MP cost, it's better to think of these costs in terms of (shared) recovery time rather than just whatever cost is pained over the hotkey. If we recharge 400 MP per GCD, for instance, a 400-MP spell is MP-neutral. The difference is simply in the tuning point for rewarding (or reducing the opportunity cost of) downtime; the higher the floor MP cost and MP generation, the less downtime punishes a healer / the more shared resource time a healer recovers during downtime.
I would guess a good tuning point is "High enough an MP floor that some downtime can still be leveraged and, if truly everything went to hell in a handbasket, one could idle a little bit to milk out enough MP for another oGCD and thereby prevent a would-be death, but where there's otherwise/generally no feeling that attacks or other filler spells come at cost."
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[Question] How "free" should those abilities be? E.g., about how much oGCD potency per minute should one be able to milk out sustainable? How long, if hitting every possible ability as quickly as possible, should it take to go oom?
(Another small note here - you can allow for a higher maximum sustainable ppm or longer minimum time until oom if you also have some MP-costly attacks that are expected to be cycled on cooldown, since they'd combine to form parity.)
