There's a lot of information missing in the search results that might be useful. However, it's important to keep the search results uncluttered, so that the focus is on the most important information.
I think unstable items would be a good idea to highlight though, perhaps with a red asterisk.
Another important piece of information that's currently missing is the kind of item. It can be deduced from the color, but that is hard to remember, even when you use the search regularly. Furthermore, conveying information only in colors makes the page inaccessible for color blind and visually impaired people.
This is particularly annoying when multiple items with the same name exist:
There's a macro and a struct with the same name. To get to the correct page, you need to remember which color indicates which item kind. Reading the description might give you this information, but not always. A legend at the top would be really useful:
That's still not great for accessibility, though. Ideally, the item kinds could be clicked to only show traits, or only structs, etc.
Unstable items need the opposite of highlighting when I’m writing for stable (which should be the default assumption). They need graying-out, or obviously the best would be to hide them altogether from stable docs. At the very least there should be a toggle to hide them. They are 100% unnecessary and distracting, and warning symbols and highlights simply make them even more distracting.