The way the game is designed now, a lot of things - HP regen, MP regen, TP regen, DoTs, HoTs, the Eorzean minute, among other things I don't remember right now - are all synced together, to tick every 3 seconds (give or take a fraction of a second due to latency). Because of that, having such ticks modify based on skill/spell speed likely won't happen, as it would require a pretty major overhaul of how the servers process information - which the developers likely don't have time for at the moment given the current development cycle.