I mean these creators can create their personal recommendation streams (of other videos they liked) and some weighted combination of those items could enter my recommendations. This feature is present in Soundcloud.

That does sound like it could be interesting, however it also sounds like it could be horrible. Just because I subscribe to a creator doesn't always mean I align with their views on everything, so could fill my feed with junk.

I guess it would have to be another setting along with the subscription flag.