For ppc32 host support the infrastructure is mostly there. What's left to do is some cleanup to build correctly, a mechanism to reserve host VSID space, guest entry/exit code and code to fill in pages in the host HTAB.
To get accel support some registers need to get moved to a common page that the guest can request to get mapped into its physical address space. Both hypervisor and guest would then access that page, always both using the right values. The patching to use that page should be done inside the guest itself.
All in all it shouldn't be hard - just needs to be done :-).
For the PPC32 host support I also put up a proposal for Google Summer of Code: http://wiki.qemu.org/Google_Summer_of_Code_2010