I've never tried the KDE connect thing but I'm guessing that it uses MPRIS2 to Strawberry and also have a service running which listens to a port which then function as a received on the computer which again the Android remote connects to.
All such remotes which uses standard MPRIS2 will function with Strawberry.
But they only have basic functionality: https://specifications.freedesktop.org/mpris-spec/latest/
The purpose of having a custom remote specifically for the Strawberry like Clementine does is to manage all features of the player, not just basic play/stop/pause, etc. It won't be compatible with other audio players.
Spotify does not provide full-length stream URL's in the public API as far as I know.
Clementine uses the official library to receive raw audio, the library was discontinued many years ago, and I'm unsure if it still works. I've only briefly looked at how it works.
But the way Clementine does it is very complicated code-wise, and the specific code that links to the spotify library (blob) runs in it's own process outside of the main application not to violate the GPL license, and is usually not included in ie.: distro packaging. So the users has to click the download button in the settings to get both the spotify library and the clementine blob code.
Does Spotify in Clementine work anymore at all?
Even if I was to work on it I would need a subscription which I need to pay for, and I'm not even interested in having a spotify subscription. It would probably require to decrypt the stream in some way and implement a gstreamer plugin to handle it. I'm not keen on using the old spotify library even if it still works, since it's closed source and discontinued.
Feel free to do it if you think it is easy.
@desputin I second this request. I came to Strawberry from iTunes, and used this a lot in my smart playlists.
In the meantime, I've found a "workaround" of sorts using the "grouping" tag. You can use this to create custom tags for tracks, then use those in Strawberry's smart playlists. Not quite the same, but it's something.
I don't want to do scraping as it will easily break if they change the website.
I have asked BandCamp for API access, they sent me this answer:
Thanks for your interest. Our APIs are currently limited to Label Accounts (bandcamp.com/labels) looking to pull physical order and general sales information, though that might change down the road. Please keep an eye on bandcamp.com/developer for updates.