I think this is a very good idea and I like the suggestion already stated of putting a sub-category in Collectibles, because that is what gachas really are. People buy, sell and most importantly trade gacha items.
It is sad that the only category anyone wants them to be in carries the stigma of the word USED.
Before I got involved in Gachas, I just recently returned to SL after a long illness, I would never even open search results in the USED Item category because of the feeling the word gives.
As for the earlier poster who so bitterly described gachas as used, no they are resale, not used. Resale items are new, with or without tag items. It is not lingerie that has been worn a dozen times then thrown on a flea-market table.
Gacha resell is a great way for people who, in RL, cannot afford a 3,000L+ bed because they live on limited incomes, The items are in most cases exquisitely designed. And are a very positive affect on inworld and marketplace economy.
Are there issues that need to be resolved, yes...but becoming bitter does not solve problems. Cooperation, communication and courtesy does.
As for the Gacha seller who did not understand, after an hour of discussion, well your just can't fix stupid. But being a part of the Gacha seller community, I will state emphatically that they fall into that 1-5% that any and every category has.
Just my humble opinion.