I think the feel from the Devs is that there isn't enough new functionality to justify the major version bump, this primarily being a reimplementation of existing features.

BUT, I agree with you, it should definitely be V11 under the semantic versioning scheme.
Whilst there is a migration path here, the database changes under the hood alone are likely to break backwards compatibility with all plugins (with in-house plugins being upgraded in sync).
Such breakage is kind of the defining characteristic of a MAJOR version.

In traditional versioning systems you only jump major versions if you break compatibility with previous versions. For instance Semantic Versioning.

Unless the media also uses HDR in which case the server will still be required to transcode.