I've wondered when something like this will pop-up. Cursor just doesn't lend itself very well to interactive data work. I actually even tried to put together something similar myself over Christmas break as a PoC: https://github.com/demirev/radian
I was thinking in the lines of something with a lobby system and the option to join other people's games. But sure, once you have a group zoom works just fine :)
a piece of feedback: please move the 'close' button on the pop-up video player to the top-right, where users usually expect it to be (ideally I would prefer no pop-up player at all, but I guess you had your reasons).
I can highly recommend RestRserve [0] for bringing R models into production (it forks every request so scaling up is easier than with Plumber). I use it regularly for various projects and I have had minimal issues with it.
Is Julia actually used that much? I've been hearing people herald it as the next big thing for the last five years or so, but it doesn't seem like it has taken off. I personally don't know anybody who uses it professionally (I know plenty of people who use R professionally). The most recent SO survey also indicates that it is rather unpopular.
Did the app really grant them continuous access to user info? I thought it was a one-off thing - they get your data at the time of use (and your friends') and that's it.
Plus the approach you outlined would require the user to like/dislike things based on the add they saw, so CA can observe a change in the predicted affiliation (they didn't have access to posts as far as I know). I don't think it would have that effect (even if the add influences you, I doubt that it would make you go unlike Obama's page for example). Not to mention that by any likelihood you shouldn't be able to verify that a particular add was shown to a given individual.
I suspect it was a simpler use case - they would group users into segments, and then craft different add strategies for each one (maybe based on other research or just expert opinion).