Hi. I'm afraid it's clear that developing the desktop controllers is not part of Sonos' plans.
In theory this could all be done by any music service provider, but few put much effort into their Search experience. For example I would like an artist search to then show albums from that artist, but few even bother with that simple feature.
BTW Sonos never sort any 3rd party content, for many good reasons.
YTM has probably the worst Sonos integration of any of the ~70 supported services, so there is zero point asking them for anything this complicated.
So the search function on any Sonos app is controlled by the music service providers, not by Sonos?
The data is, yes. Sonos sends a request to the music provider, then displays what the music provider sends back.
So the search function on any Sonos app is controlled by the music service providers, not by Sonos?
Absolutely. Only when you search your Local Library is Sonos code exercised.
For music services, Sonos first asks for a category list (these are shown as tabs in the Desktop app). Then the search string is passed to the music service, along with the category-id, and the service delivers a list of results. On the mobile controllers multiple calls are made to multiple services with multiple categories, and the results mashed together.
Full details at https://developer.sonos.com/build/content-service-add-features/add-search/