Hi,
If you're looking to pull in 32bit pcibios support, then I don't think it would be worthwhile to rebase to a stable branch, as the 32bit pcibios support is easily the biggest user visible change in v0.5.1 (in the sense that Linux will call 32bit pcibios if it's available).
Unless there's a strong demand for it, I'd like to hold off on 32bit pcibios support.
I think someone mentioned bochs-based pcbios in qemu 0.11 has 32bit pcibios support, so not having that in 0.12 would be a regression. Dunno how much this is a problem in practice though.
cheers, Gerd