Too many times I've seen what is definitely trash content - memes, dancing videos, AI-narrated "did you know" videos, etc... very low effort and low quality.
If shorts were a gateway or lead-in to longer videos (like a preview or highlights), I'm all for it. A quick example of the channel's style of explanation or what their content is all about. For example, I'm into cooking - If a short was like 15 seconds and said "hey, here's the recipe we're going to make today, and here are the ingredients, watch the full video for the full walkthrough", I'd be all over that. Same could be said for other things I'm into, such as music production ("here's a quick overview of how I made the lead sound for this song, watch the full video for the song breakdown") or economics ("Argentina goes into hyperinflation every decade or so, watch our video for a more detailed explanation of how and why").
Shorts could also be quick tips or interesting things like that. There are a few sports-related channels that provide instructions that can be summed up in less than 30 seconds and don't need a detailed explanation. I find those to be really useful. The famous tennis coach Patrick Mouratoglu is a good example, some of his shorts are great in that they provide simple fixes to issues a lot of tennis players of all levels (including some pros!) have in their game. Have an issue with your serve toss? Do this drill. Have an issue with your net game? Here's a simple drill to fix it. Easy, and straightforward. You learn something quickly, and you move on.
Short form content can be really useful, but it can also be bad in that it's too much junk as everyone wants to be a creator yet doesn't really have interesting content to learn from.
While they're at it, maybe they could consider an option to remove all "upcoming" / "notify me" items too, so only showing video thumbnails I can click on and, you know, actually watch a video?
An additional option to avoid "mix" thumbnails in recommendations would be another win, as far as I'm concerned.