I'm not speaking for the QEMU project. I hope to be helpful anyway. I am the QAPI maintainer, so my thoughts carry a bit more weight there.
I understand your block driver depends on your libvitastor_client library. Dependencies that aren't available on at least one supported build platform (and thus covered by CI) are problematic. For Linux, "available" generally means "provided by the distribution". I doubt there's a way around getting your library packaged by distributions. The QAPI schema is (for better or worse) fixed at compile time by design. Changing that would be a major undertaking. Whether the benefits could justify the costs and risks seems rather doubtful to me. In my experience, the project invites contributions, not out-of-tree extensions. The latter require external interfaces, which can only be harder to maintain than internal ones. There's also the risk of abuse to circumvent the GPL (I have absolutely no reason to assume you'd try that!).
