So the conclusion would be that for inclusion in mainline:
-The xen dom0 interface should be clean, and the code self contained
-Backwards compatibility of the hypervisor is no argument to include
anything in mainline (and if desired, should be realised in the hypervisor
by (temporarily) supporting the old abi for the current xen specific
kernels and one for the mainline kernel, and thus placing the maintenance
burden of that desire on Xen and not the Kernel)
--
Sander