Joshua, IMHO the system you are proposing is not a natural one for standard roguelikes. It means that, for example, you get to move 4 times, then your enemy gets to move 4 times. I see this as less natural than the standard roguelike movement, which makes you alternate turns.
It can have some use to minimalize "context switching" between player characters, for either party-based (Exile/Avernum which is quite close to roguelikes used it) or multiplayer games (War of Wizards 7DRL? I am not sure). I also remember Lair of Demon Ape use something similar to action points.
A natural way is to have each being have a T value, which means, when will it be able to perform the next action (in global time). After each action, we find the creature which has the smallest value of T, set the global clock to T, let it do what it wants, and increase its T, which can depend on its speed and action. The system proposed by Gamer_2k4, and also used in ADOM at least, works similarly but is more complicated than my natural system, I guess in order to make it more effective, although it sometimes adds some weird behavior. (However, my system can be implemented effectively, in O(log n) per action, where n is the number of creatures.)