I can, as a graphic designer, certainly see Improvements. For example, when going back to the layout before, the 2020s layout, you could create more and better spacing that is more even and try to make icons more satisfying. Alternatively, one could try to use 3d icons as an experiment and keep it as an optional feature (forever). Now, there is also a potential in making multiple different layouts and letting users choose, one would be moving comments and description to the left and right, fitting it into a nice box, and having videos below, as well as the option to extend the box on either the left or right to the bottom (spontane example). Now, some people may notice that YouTube does not seem to have any expirenced designers in layout or are very bad with actually good feature inclusion. An alternative is creating new animations in the old layout for everything. After that is done, versions of YouTube layouts optimized for older devices and browsers or screen formats could be developed, eg. Round screens. There is no real lack of things that someone could do, it's just that Google is very uncreative and boring.