Following up from a comment on the blog, you asked that I discuss my concerns about the way Plex integrates with Sonos in the context of these typical concerns:
(A) the current Plex-Sonos service is broken for me, and it seems like the "cloud" service provider might be responsible
(B) the current Plex-Sonos service feels slow, and it seems like the "cloud" service provider might be responsible
(C) from a privacy perspective, I don't want my music library information to go through Plex
(D) I have a Sonos in a location that has no Internet access, and I want Plex-Sonos to work there
I don't have any issue with (A) and (B). I'd say (C) is a minor concern, though like most members of western civilization in the 21st century, I've long given up on the idea that I actually have any privacy. It mostly has to do with (D), and (E): complexity, and necessity.
Bear in mind I have long, long history with streaming music. I was one of the first owners of a Squeezebox back in 1995. All I have ever wanted out of Sonos is to be as good as that was, 20 years ago. I only got a Sonos a couple years ago because it because too much effort to keep the Squeezebox stuff going -- from both a hardware and software perspective -- and there was no support for modern streaming services (other than Spotify). Generally I have been happy with that decision, but I miss many things about my old setup. The basic service and features was actually much better than what I have now - in terms of plugin support, flexibility, quality, apps, and even remote access.
So I have to think about this holisitcally. If my internet service is down, I can't play my music. If you (Plex) decide to end your partnership with Sonos, I can't play my music. If you go out of business, I can't play my music. If your cloud service is temporarily down, I can't play my music.
At the end of the day, the necessity to interact with a cloud service to just play music using a client that can work without internet access (Sonos), from a server that can work without Internet access (Plex), in a closed network, seems silly and adds a significant point of failure with many dependencies. Sure, most of the time everything will just work, but there will definitely be times it does not, and I expect it will be when I'm having a dinner party and it'll be really annoying.
Is this going to be a dealbreaker for me? Well I already have a lifetime Plex pass so, obviously not, I'm glad for the service. If you can improve it to be a lot better than Subsonic is now, e.g. by adding Genre support, better scanning (e.g. show the letter while scrolling), and in my fantasy world, add some Logitech Media Server-like features such as plugins for creating playlists dynamically, then I'll most likely switch to Plex as my primary private library server. Though I definitely won't uninstall Subsonic from my computer so I have a backup plan. It's just a bit disappointing to have something that ought to be nice and clean have a whole bunch of external dependencies.