Based on the blog posts & diagrams linked here, the main innovation seems to be the use of virtio as a transport mechanism for the high-level "accelerated" functions. The portable API is a good idea, but could just as easily connect to a well-known gRPC service address (which could be always on-host, or not). In that case, the transport would be good ol' virtio-net (or whatever), but is otherwise the same to the user.

I suppose that with virtio, you can perhaps eliminate one copy (but not necessarily, since you'll probably need to copy from the guest memory into some device-mapped buffer). Other than it being fun to write virtio backends for various hypervisors, I'm not sure what the compelling advantage is over the more naive transport? Perhaps I'm missing something.