On release of clothes, have a simple sackcloth robe or onesie available for cubits
Add a new currency that can only be purchased as RMT
When you release new clothes and cosmetics and tattoos, make them purchaseable only with RMT currency, but 3 months after cosmetics come out, switch them to be purchaseable with cubits. Also, as clothes and cosmetics get “older”, their prices should go down. This is not only nice for newer players, it makes older cosmetics “common” which encourages people to buy new cosmetics. People love the hottest new thing. You should see the “dumb” sht people spend fortunes on in GTA, ESO, WoW etc. Seriously, people spend thousands of IRL dollars to have the hottest new outfit every month.
I’d say leave event cosmetics as-is.
This is what a lot of other games do, and I think it would be fair. Especially if this is what it takes to get clothes, and if nothing remains a RMT exclusive forever, I’m down.