It's far from efficient then- I mean, if you end up culling half because they are male anyway, yeah you'd end up finishing in half the sites. But I'd expect that you'd want to initiate flower at a VERY small size, and that might not even be possible, because sexual maturity has to happen first. Maybe an autoflower strain would work?
I don't know...it seems like a lot of 'ifs' and not a lot of flexibility.