It seems to me that you are mis-reading the RedHat bug ticket. What they are saying (as I read it) is that VirtualBox should work with virt-manager, and that if it doesn't they are at least theoretically ready to fix the problem, but that for policy reasons they cannot support it officially - namely that they only officially support hypervisors which are a default part of the host operating system, like kvm in the Linux kernel.
That said, I think it very unlikely that we would be willing to make non-trivial changes to our product purely in order to make virt-manager work better, simply because it is not important enough to us, and all our developers are fully occupied with work which is important to us - and I doubt this will change in the foreseeable future. We might well accept user patches if we were convinced that they had been well tested by enough people. As no users seem to be interested in submitting patches I take it as a sign that no changes are needed.
