I think for blackmage (and maybe all classes) it would have to be a universal set for main skills. Like for Blackmage, you could choose a buff to potency for Ice (tho fire being far superior still) or you can increase the duration of your Umbral/Astral by say...3 secs? One would be good for learning (or casual mages I guess) while the Ice buff would be basically what we have now but stronger ice skills. Same with healers and more potency vs longer ticks for HoT. Maybe some DPS could increase the time Dots stay on vs say Huton/Greased Lightning having increased timers. Just a lot they could do with it but ultimately in the end sounds like a balance nightmare for them to do.