In other games, I rather like a hybrid of the Hero System version, where different characters have different "speeds" (SPD) as a stat, and thus move more or less often in a given time frame. Hero puts this on a chart, and makes it rigid. They way I like to play such a system is to let everyone attempt to go each "round", but require a check based on SPD to pull it off "right now". If you fail, you get a bonus to your next check, as long as you keep trying the same thing.
The variant we used with Hero was to have the GM roll one die for all participants. Then you compared your SPD + mods to this roll each round to see if you went. The effect is one of controlled chaos, where actions tend to average out over a fight, but you rarely know for sure who is going next.
I haven't tried that with a version of D&D yet, but I could actually see it working better in Next, as a side-by-side variant, than it would have worked in other versions. The flatter math helps a lot. Declare your action (broadly). When your side is up, roll your initiative check. Make it, you go. Fail it, get something like a +5 mod to your next check if you stick with your declaration. (Mods are cumulative, but go away when you succeed on a check.) That's a variant where everyone could go each round, but most rounds will catch someone in mid action.