If it could be programmed in, so many awesome things could be done. Buffs that morph into debuffs, debuffs that morph into heals / etc., buffs that cycle, debuffs that cycle, on and on the list goes. I thought it'd be how recursive curse works, but, um, nope? Basically, it'd open up entire new lines of thinking for mods. Imagine a defensive buff that heals when it gets knocked off after a number of hits, or some hyper-offensive buff that makes you explode after you get hit (I'm thinking of the currently-existing radiant mage mod). Delayed heals or damage spikes (oh there's a boss monster deep in the zoo? I'll have time to wait the 20 turns for this damage spike to go off...). I remember I used to play EQ, and the game instantly became significantly more interesting when they finally coded that in - both encounter design and player abilities drastically changed. I, however, have no idea how difficult this would be to impliment.
Well you can have it as a timed thing, and that's entirely possible at the moment without this. But otherwise I know this has already been suggested but I guess it brings the idea up again.
Ah, my bad. I am pretty new around here. I just found the "modders request thread" about 5 minutes ago, and whoops, that was embarrassing. Anyway, I was thinking of a capstone which had an upkeep cost but cancelling it was a heal (and cancelling maintained buffs doesn't use your turn, does it?). So it was along those kinds of lines: not specifically timed. Oh well. I can live without it.