The problem is timers though. There are too many timers on DDO. Elixirs have a timer, raids have a timer, chest ransack have timers, character buffs have timers, summons have timers, even quests have timers.
That's a good point and tracking those things as well as firing off events, I suspect, would use a considerable amount of resources (even if it is a small overall percentage).
I've played a number of other games where, instead of potions that gave extra xp over time, the potion just granted a set amount. This is similar to how the saga rewards and dice rolls work. I realize that would only increase the "pay to win" feel, but it would potentially cut down on system resources as well as alleviating the feeling of wasting money on a potion that is counting down while lagging or running to a quest in a wilderness.