This idea isn't half bad, I say "half bad" because this system you have mentioned would be easily exploited. Personally just buy reading it, I thought to buy worthless Howlite's and revert them for their fusion power ha. If it reverted back into the materials it took to create that particular gem stone would be good. Then maybe we could sell gem stones to that particular NPC for fusion powder. The higher the tier; the more fusion powder we get.
Reverting gems cannot be absolutely free though, can it? It'd have to take some type of skill, or money or... a Reversion Shard, bought from Gem Supply, in the fusion house ;D. Just an idea.
+1, after suggestion is refined.