-1 we pay for the looks (expansions)
and ability to be compatible with a paid set. (ABC)
Just like any game (in-game / in-app purchases or DLCs) are what helps make the games' players feel a sense of diversity.
If I saw some expansions with people who didn't pay for them and look at my paid one then you'd feel either run out for your money or your expansion doesn't feel much of an expansion anymore.
Supply and demand like what most people are stating will take in effect and I rather see GMs working on fixing bugs, playing events with the community more, having field days with players, or developing storyline/quests then working on copying an expansion to the vote system
(if anything there are some headgears that were in iRO which used to be good stat wise, maybe someday when things like economy and connection here becomes more stable then GMs could implement those. (Robo eyes, mall items given better stats and made vote)
This is only my opinion but regardless it's good you made a suggestion. :)