So I would need to run a spare reg on both sides or have a QD attached so that I can change out the reg to the good side. Did I get that right?
I think you've got it. The Z system seems to me to be a complicated solution to an almost non-existent problem. So far, I've always set up my sidemount system for mixed team diving, with a a long hose on my right tank and a short hose with a bungeed second stage on the left. I'll donate the long those if I'm breathing it, and unclip it and donate it if I'm not. If unclipping it takes too long, or a panicked diver grabs it while it's clipped off, it will come free easily, since the bolt snap is attached to the hose via the little break-away gadget that Go Sidemount sells. When it comes time for the advanced course and tighter restrictions, the long hose will be replaced by a second short hose, since there won't be any backmount divers in the area.