A setting or option to play any video link via a preferred site like vimeo, invdio, etc. if the user happens to post a youtube link?

It's possible, but difficult. It can be hard for software to tell if 2 videos are "the same video" unless they're completely identical, and even then it might be hard because the different sites might have different ways of compressing the video so even with the same video you'll get slightly different outputs.

It's a cool idea! Just not sure if it's actually doable because of how hard it is to find "the same video" with software, but it might be doable nowadays. They're certainly able to detect replications of videos on youtube for takedowns... so I guess you could probably use the same video comparison software...