One advantage I can see for bringing more providers into the core is the cost of acceptance testing. As a developer of vagrant-libvirt I really hope to add both

One advantage I can see for bringing more providers into the core is the cost of acceptance testing. As a developer of vagrant-libvirt I really hope to add both unit and acceptance tests in order to catch regressions. Some are caused by goofs on our part, and others are caused by changes in newer vagrant versions. Even if we had good acceptance tests, we wouldn't have a CI environment to run them in (we'd need either bare-metal or a VM with nested virtualization). I assume that Hashicorp has invested in such an environment for providers in the Vagrant core that they are commercially supporting.