I agree this would balance U/U and crafted gear. However, this would be a nightmare for linkshell leaders. Think for a sec if in FF11 you could meld Ridill and E.Body. People killed themselves just to get one copy of these items. What would happen if you wanted to obtain 10 of them to double meld? Not a fun situation to think about.

Other solutions have been mentioned so I won't go there, but I'm in favor of giving U/U items one free slot and limiting crafted items to 2-3 slots.