If you search you’ll find this subject has been discussed to death, unlikely to happen…
Spotify has 443 million users (188 million of them paying subscribers) at the last count. I very much doubt they could care less about a niche music delivery platform like Roon.
I expect Spotify ambitions lie much more in how content is generated and licensed and how they can over time create audio content that they fully own the rights to — much like Amazon, Netflix and Apple+ are increasingly generating their own content rather than buying it in.
In terms of delivery they already have Spotify Connect (which is widely rolled out) and a suite of native apps and a web-based player that I expect works just fine for 99% of their audience and gives them tight control over analytics and the user experience (aka pushing certain content).
Where Roon could possibly look at integrating with Spotify is Playlists.
I could imagine a feature in Roon where you could login with your Spotify account purely for the purposes of sharing (syncing) playlists.
In much the same way as you’d login to Spotify on Soundiiz or TuneMyMusic to do the same thing there. But instead of having to manually export your playlists from Roon and then upload them to a 3rd party service (which may have additional costs) you could do it directly from within Roon ie. select a playlist in Roon and then share it via your Spotify account or import a Spotify playlist by cut and patting the public Spotify URL into Roon.
Obviously the tracks on that playlist would still stream from Qobuz / Tidal (or your local library) and would rely on those tracks being available. But that’s no different to how things currently work if you used a 3rd party service like Soundiiz outside of Roon. It’s just that you’d now have that feature integrated more tightly within the Roon interface.
You could extend that model to other services, Qobuz / Tidal being obvious candidates. But I think the key benefit to supporting Spotify for playlists is the ubiquious nature of them.
If someone shares a playlist with me 9 times out of 10 will be via Spotify, if a magazine does a ‘genre introduction’ it’s likely to be in the form of a Spotify (or maybe a YouTube) playlist embed in the page, if a festival does a selection of tracks from artists that are playing at that festival, again it’s likely to be a Spotify playlist, if my favourite artist or friend does a mixtape/playlist again it’s likely to be a Spotify playlist.
The same is true if I want to share a playlist, if I send a general friend or work colleague a link to a Qobuz playlist — you can’t even send a link from within the Roon interface currently — they probably won’t know what to do with it. But if I send them a link to a Spotify playlist they can play or save it (and maybe convert it to another platform later) even if they aren’t a paying Spotify subscriber.