something I've always wondered:

why hasn't anyone built a fully-featured desktop Youtube front-end experience? With, like, borderless floating video (a la Firefox's floating video feature), dimming the desktop, a search experience that doesn't bombard you with clickbait garbage, etc?

it seems like Youtube.com is really just a fancy mp4 player, targeting static video content.

does Youtube actively do anything to prevent such clients from existing? What's their stance on them? Will they one day change the service so the video stream urls are generated randomly, or obfuscated, and break every 3rd party client?

Not really, no. Though they took some kind of legal action against Hooktube I remember.

> Will they one day change the service so the video stream urls are generated randomly, or obfuscated, and break every 3rd party client?

They already do this to some extent for videos with copyrighted content, but it's not very aggressive and has long been reverse-engineered and dealt with. They use a series of three string transformations like reversal, replacing a single letter, etc. on an alphanumeric signature parameter. The sequence of transformations varies per video but can be extracted from the Javascript source using regular expressions.

Here are some available clients I know of. I do not know if there any that use floating videos or dim the desktop as you say:

mps-youtube (terminal-only): https://github.com/mps-youtube/mps-youtube

youtube-viewer: https://github.com/trizen/youtube-viewer

FreeTube (which uses the invidious API): https://github.com/FreeTubeApp/FreeTube

Invidious: https://invidio.us/, https://github.com/iv-org/invidious

youtube-local (my project): https://github.com/user234683/youtube-local

smtube: https://www.smtube.org/

Minitube: https://flavio.tordini.org/minitube, https://github.com/flaviotordini/minitube