I'm rather fond of just using target for your actual target, i know it seems like a novel concept any more. :P

And for setting that target, i just have an FTL style button, which basically uses a "targetexact" for any one of the 5 based on who's current main, and then assists and just leaves the assist target up. This is very easy for PvE, I can understand there might be a good reason not to leave a target up in PvP, but i don't do it. It also lets me keep dpsing the same target i've got all my tank's threat against while the tank can feel free to swap targets and build up a little pre-agro on the up and coming target, or and new mobs that have come along and like the healer a lot.

I do have to hit the button each time i want dps to change targets, but really it's not that hard to do. And since the target button is FTL, I can just start driving from a new main at any moment. Of course, having innerspace automatically rewrite the targetexact macro for the group i'm playing when I load up the team is really what makes the whole thing an option in my opinion.