I'd move to allow it rather than waiting for some "critical mass". Retroactive changes suck, and if providing a video legitimately improves the question, there's no reason to exclude it from the get-go.
That said, if a video is all that is provided, raise the pitchforks and downvote the answer to all hell. It's the identical problem with link-only answers:
- The external content could rot, so the answer can become completely useless
- The part relevant to the answer is maybe kinda sorta indirectly somewhere on the page, and without context, or couching in terms of the question, is useless.