QUOTE (SynthesisRTF @ Aug 18 2012, 06:57 PM)
It does sound like a more unique idea, and it can make battles a lot harder, thus increasing challenge.
You're going to have to change the menus around to remove data about current HP and MP though.
I think that's not required. You should be aware of how many HP/MP you have at the beginning of the battle.
Since HP/MP will rise with level (or at least I suppose), I think it would be better to show them anyway.
Obviously, with a full heal feature like this you can effectively make battles more complicated.
If I were you, I'd give a look to this project, in which the author implemented the feature you were talking about:A Dust Tale
If you are planning to use that system, you will have to do a lot of work on enemies' AI to make every battle very challenging.
Anyway, I'm for this idea, I've made something similar in one of my previous projects and worked quite well.
So... keep on your way, it's a rather good idea.