Firstly I’d like to say that Plexamp changed the way I interact with my music collection, I’ve refound artists and bands I’d long forgotten about and when I look at my server stats, music, and my toddlers tv, are far and above any other media. You should be incredibly proud of that application, thank you!
Thanks for the kind words, @richardap1! As one of the folks on the team that uses Plex mostly for music, I have a personal interest in helping make that experience the best it can be. There are many ways we can improve yet, but we are proud of what the entire team has built so far, and we’re happy that you’re enjoying it!
To your specific points…
Is Plexamp going to move out of labs and become a “full” Plex product?
Yes! Well, technically, it already has!
We didn’t state it explicitly in our July announcement about Plexamp now being free for all users, but extending access was a necessary step to graduating Plexamp from being a Labs initiative to a fully-supported client app.
Are you looking at other ways of monetising the music element of Plex and Plexamp, with integration with other streaming services
Integrations with other services are challenging not only from an API perspective, but also contractually. We’ve definitely had wishlist ideas, but we’re not working in this area currently.
if I Play a track from an album, and I have two versions of that album, standard and deluxe, then both appear in the stats. Being able to group releases would be excellent.
Apologies for getting slightly into the weeds a bit here…
But yeah, two copies of an identical track will share play counts (“identical” meaning MusicBrainz considers them the same recording and they matched to the same GUID). We don’t store which specific instance of identical tracks you listened to. This is by design — and is helpful in scenarios where, for instance, you replace an album in your library with one of a higher quality; we’ll remember the plays the tracks had before, because they were stored by GUID and not tied to a previous track ID that’s now gone. It’s a design choice not everyone will agree with, but to your larger point… yes! We’re always looking for ways to improve library management where we can. 
I’d love to see more artist cross connections, for example the metadata for artists and albums contains numerous references to other artists, bands and albums. It would be great to see those hyperlinked so we can jump between objects.
Yes! I really want that too! The linking from artist biographies in particular though is a tricky problem. Say there’s a reference to another artist that doesn’t exist in your library. Where would the link point to? Would access to TIDAL affect it? What if it points to an artist on a shared server? What if you have access to that artist on multiple servers? What if that access changes? It gets… complicated. 
It’s not impossible, of course. I agree in principle that having that functionality would be useful!
finding new material can be tedious. I know Tidal integration helps here, but having a section for similar artists that are not in my library would be great.
Totally agree! We surface recommendations like these in Plex Web — for instance, on an artist page we present Plex Recommendations on TIDAL and Artists You Might Like (from shared servers) which are artists similar to the one being viewed… but we don’t show those specific content rows in Plexamp, and off the top of my head, I don’t recall exactly why… 
But I’ll make a note to investigate. I agree that those, or something similar surfaced on Home would be helpful here!
Thank you again for your feedback!