I think there is a bit of a tradeoff here, if we do use SSA eventually... namely, the unused complexity it adds to vsir, versus the cost of asking Conor to rewrite his patches just so he can un-rewrite them later. I'm still inclined to say the latter outweighs the former, and if that means we have to wait for 1.9 so be it. But I won't belabor the argument.
Right, at this point the likely scenario is that we'll release 1.9 without dxil support, and then commit this MR more or less as-is after the release. That's unfortunate though, and I don't think it necessarily had to be that way. Perhaps more importantly, I'd also like to make sure we try to avoid similar situations going forward.