MusicBrainz allows to link an artist to their Last.fm, such as:
https://musicbrainz.org/artist/5873cd12-ac72-407b-a79c-1f9f9682e239 -> https://www.last.fm/music/Neru

But at the same time, there's no way to link a specific recording, such as:
https://musicbrainz.org/recording/e5d2c049-589d-4ac6-bb41-a155a57da0b6 -> https://www.last.fm/music/Neru/_/%E3%83%AD%E3%82%B9%E3%83%88%E3%83%AF%E3%83%B3%E3%81%AE%E5%8F%B7%E5%93%AD
or album, such as:
https://musicbrainz.org/release/fdbbe2b3-5717-4fd9-84ce-54128c6a41fe -> https://www.last.fm/music/DECO*27/GHOST

MusicBrainz displays an icon with Last.fm logo, but asks to select the type of relationship, none of which apply.

I believe this kind of relationships would be useful for the ListenBrainz project, and it could be used to determine more external streaming URLs.