I think it needs to be on a seperate chain, the volume of data through it will be massive plus the nature of the content I believe will benefit from seperation. I'm getting worried about the whole SMT situation, there's been no news for months (not uncommon for steem though) but also no real announcements of partnerships for SMT's.

I really think that Vice will just be Dtube pointing to a different chain. The product should be 100% available to start working on day 1, the chain works everything else works. So long as the front end works they'll be 100% operational on day 1.
It'll also allow for witnesses to spread across different chains, those not making much here can head there to increase their chance of better witness rewards I'd assume.