I've wanted to have this since the site launched this January. It should be a big help in keeping down the # of videos on the site with no working video links - some studios and directors only upload to Vimeo, and many other videos can be found only on Dailymotion (although it's probably better not to use Dailymotion if there are other options, because apparently the whole site has been blocked in Russia since 2017 because of some copyright case that year).
To test it out, check out the DIY page:
In the coming days, I'll be going through the site and adding some videos that can only be found outside of Youtube.
In theory, any video website with a public player API/SDK that will send information about the current time in the video can be added (preferably also start/pause events, video loaded, and video ended). Many sites lack this ability, however. I would like to add VKontakte, Odnoklassniki and Bilibili, but it seems impossible.
The easiest site to add next would probably be RuTube, or perhaps Archive.org (which uses JWPlayer, so maybe it's possible?).
The other reason this is important is because Youtube has been deleting various prominent Russian channels, and if relations between Youtube and the Russian government continue to worsen to the point of Russian film studios being instructed to close their Youtube accounts (which seems possible in the future, though goodness knows it would be an unpleasant shock for the studios!), it would be good to have alternatives.
P.S. If it doesn't work for you, you might have to press Ctrl+F5 to clear the old site files from your cache.