At current prices, pledging $5 worth of storage while the app is installed is enough to cache 20 hours of video. It's not too bad.
> the last thing I want is to use some unknown, unpredictably changing residential connection for my videos
YouTube only buffers a handful of seconds. Let's say other users would only be used to buffer 30-60 seconds in the future and if it drops below 15 a fast server is used. Does that solve your worries?