The update sounds good. As far as UI goes, I think game devs are going to want to customize that a lot, but there should be some similar underlying mechanics. For me, basically I want players to either get a skill as a quest reward or buy one with credits from a vendor. The skills they get as rewards are less likely to be as desirable as the ones they save up for and buy, but they help the player progress. The newly acquired skill is not activated till they spend another type of credit to place a modifier on it. Display-wise, since there's three modifiers, there's three columns on screen and the skill gets placed into whichever one matches the modifier. After that, the skill is available to be added to the action bar of the player. I don't know if that helps any. To me, my design shares similarities with your examples. I'm thinking that a lot of different skill scenarios can probably be created by using the vendor / inventory / category features that likely already exist in the system.