Open Stack

Remove everything out of tree, and leave only Neutron API framework as
integration platform, would lower the attractions of the whole
Openstack Project. Without a default "good enough" reference backend
from community, customers have to depends on packagers to fully test
all backends for them. Can we image nova without kvm, glance without
swift? Cinder is weak because of default lvm backend, if in the future
Ceph became the default it would be much better.

If the goal of this decomposition is eventually moving default
reference driver out, and the in-tree OVS backend is an eyesore, then
it's better to split the Neutron core with base repo and vendor repo.
They only share common base API/DB model, each vendor can extend their
API, DB model freely, using a shim proxy to delegate all the service
logic to their backend controller. They can choose to keep out of
tree, or in tree (vendor repo) with the previous policy that
contribute code reviewing for their code being reviewed by other
vendors.