It sounds like a very compelling idea, but I'm not sure why you would put an actual cap on it at all.
Might as well let a level 1 player use a level 20 item.
Or maybe the effect you're going for is the technology being so incredibly advanced that you simply can't fathom how it works?
Maybe it would be interesting that you would need to have someone explain to you how to use certain types of items, or at least see someone using it.
I must say, this thread along with your previous one has gotten me quite curious about your game, how is development going, if at all?