This looks interesting. I just have a few questions:

I don't see why the keymaps are needed. Won't it work without them?

Have you done any damage testing of targettarget vs /assist focus? Just wondering if there is any lag difference.

What happens when you need to talk to a vendor or questgiver? Now you need another button for assist, and then you'll lose target on your leader. How do you deal with that when you play?

I also don't see why you care about harm/help (in the first two examples). Does it really make any difference if that logic is in the macro? You can't heal a mob and you can't attack your party, right?

This otherwise looks like a nice alternative.

-K