In ListenBrainz we have a fake 'unified search' interface. With a real unified search having been discussed since ~2011, and being a common request to this day, I think the LB approach is well worth implementing in MB. Even if we replace if with a real unified search in another 15 years!

In the LB interface you enter a search term and it shows you one entity search result - but with tabs for the other entities. Because clicking on those tabs only takes a second, and results load pretty quickly, it actually does a great job of feeling like a unified search, or at least giving similar convenience:

Current MusicBrainz search results:

Proposed fake 'unified search' results:

I tidied up some basic text placement and formatting as well, to make the results a bit more user-friendly overall.

The 'toggle' style buttons are new to MB, but they are critical to giving the illusion of a unified search! Rather than having them styled as 'links'. The button style can be copied directly from LB.

MB has a very long list of search entities, the best way to tackle this is probably a default collapsed state with the most popular searches, with cookies that remember if it's collapsed or expanded: