I would be okay with a monthly fee or a cash shop that doesn’t impact the entire server selling overpowered items. Service items are okay, like: inventory expansion, character name change, sex change, in ToS’s case new Lodge layouts, for a higher price you could throw in exp boosts (50% tops) and very expensive stuff would be like skill reset, stat reset, people have been talking about a rank reset as well and stuff like that. New costumes that doesn’t give any sort of status bonuses (cosmetical) are okay too.
It’s all about comunication between the companies involved (IMC + Publisher) and the player base.