Original plan for this concept was simple showcase for que-up songs using embed links to prevent autoplay playlists & ads.
Also kinda "gray area" but you don't include (redistribute) any music inside package, so no worries about copyright/license? 
I'm no legal expert, but I have tried to do a little reading on the subject because of what I want to do with it.
If it's a link to an official or otherwise licenced source, you are effectively just giving them views. Granted embeds do skip adverts, but if they have not disabled that feature, it's hard to see it as anything but tacit approval. (There are a number of channels that do disable embeds for this reason, such as the official Formula 1 channel).
They did after all host that content on Youtube for all to view and/or embed into their forums pages and websites. That's why we can add these links to our scenes in the first place.
If the VaM scene in question was behind a paywall however, that would probably be a different matter. You are at that point profiting directly from their work and they would, I imagine, be well within their rights to claim a share or block you. Not something I want to test tbh. (nor a potential problem I want to cause for Meshed and the Dev team either)
^Not that I think they would actually notice anyway, but to invent a proverb: "Don't go around kicking wasps nests when you don't have to".
(Maybe worth noting a handful of creators have seemingly been doing this anyway for some time now, by actually including the mp3's in the scenes. They are just distributing them via Patreon rather than hosting on the Hub itself. Can't say I have a problem with it, but....shall we just say they are perhaps braver than I?)
Re: the other technical stuff about volume, scrubbing etc.
I think the only elegant solution to that would be a plugin. But I'm genuinely not sure how technically feasible that actually would be. (I'm essentially just a musician and film maker. Actual coding is kind of straying somewhat into black magic for me)
If this ends up being something I do a lot of, I might approach one of the more talented programmers for a commission job. (If it even can be done)
I have a feeling it'd still be pretty limited though.
The big deals for me would be:
A. Broadcasting the audio from a web panel via an audio source. (Allowing volume, spatialization, rhythm sources etc.)
B. Some way to automate interactions with the web panel GUI. e.g. trigger a click at a specified set of co-ordinates on the screen. (that could at least cover play/pause without page loading lag, if not even a bit of timeline scrubbing.)
Anyway thanks again. This has all been very useful to me regardless of the limitations we are both banging our heads against
