phatbeetle--if you hold entry clearance, you can register for Iris, and go through the quick queue. I have done it. It's great! (unless you get held up behind a really uncoordinated person as I did last time).
In fact, I was really surprised to find out that one of my colleagues from the US was able to register for Iris without having entry clearance, but just based upon the fact that he travels to the UK so often for work. So I thought this kind of procedure was sort of already in place (for business travel, anyway)--just not widely publicised.