A lot of people would get mileage out of this. The only downside I can think of is that it would risk tanking the Leppa economy, but that's still got other uses anyway. Maybe it's still fed by Leppas, but at a much slower rate than it currently is.
The point of these Ocarinas is convenience, so not having to carry around a slave. That means this wouldn't quite work like the others, because the HMs represented by those (Fly, Cut, etc) are infinite-use. I don't have the answers right now, if anyone feels they would have a solution that involves keeping the Leppa economy alive (and not ruining it for those that have put a huge amount of time into farming them) whilst introducing what seems to be a pretty commonly-requested item, I'd love to hear it.