I don't think anything like this will ever be made by 4anime.to, as it's far too much work and is also a lot more difficult than you might think.
However, there are sites that already do this and work for any page. My personal favourite is Metastream.
omg, IT'S TOTALLY DEAD!!! mediastream is definitely what you should download next. oh hey. i just found out i've been calling it the wrong thing this entire time. IT'S METASTREAM. https://getmetastream.com/ do this!
I completely agree with you - right now https://getmetastream.com looks the best, but I think the browser extension is a turn off for so many people.
As for Kast.gg - it really seemed promising, but it just lacks that web interface.