No.

You’d need to use the native app and cast to Sonos. 

that is something I would like to avoid, as it would mean I have to pass through my phone when I could just be streaming over wifi.

perhaps something like this can be added in the future to the Sonos app, if the Tidal app has it, it should mean it is possible and only a question of implementation.

And business priorities and development resource availability.

This is never “just a few lines of code”...

what I mean is that there should be no great technical difficulties, since it already exists in some form in a partner app.

But you don’t know what API exists between Sonos and the service, so “no great technical difficulties” is another assumption. 

I’ve actually used the Tidal API pretty extensively, and don’t remember seeing a way to enable that…

https://github.com/Fokka-Engineering/TIDAL/wiki

I’m not sure whether Sonos currently supports Tidal Connect, but if not, they certainly should consider it.  I use it sometimes to my WiiM Mini from a Chromebook, another thing Sonos really ought to support, but doesn’t.  The native streaming apps are generally much better than the simplified apps from Sonos, BlueSound, etc, IME.