I mean it's not like it couldn't be done in an interesting way, but I also feel it's genuinely one of the most interesting abilities in the WHM kit, given its short duration, very strong effect and limited applicability. It's the equivalent to using your +20% buff, just in even more extreme.

The problem is of course, there's rarely~never a time you need more healing output for more than 1-2 casts. Making the vast majority of this go to waste, and hence why Horoscope etc feel much more useful in practice. They should not, if healers actually had a lot of healing to do.

As a passive trait, I'd envision it something like this, akin to the smart heals DAoC had:

"Any time you cast an group or multi-target heal an extra 800 potency heal is intelligently split between characters healed, prioritizing characters with lower health. This effect can happen no more than once every 20 seconds, and will not trigger if no one healed was below 50% health."

(also what's with the weird name for it?!)