This is my favorite combo. Best apps for general use. Interstellar is better for image posts since it's the only Lemmy app that supports masonry layout.
Personally, I've always been a big fan of Sync for Reddit / Lemmy, and Thunder for Lemmy is the closest thing I've seen yet, so that's my daily driver on Android. On desktop I use Alexandrite.
I would love to see the OS share. I bet us Linux users are all over it, since right now it is the only tool we can use to do all of that in the same place and easily.
I just avoid using "source available" and software that has artificially paywalled features, the most common paywalled feature is OIDC because most devs seem to think that it's a business only feature.
I pay for Home Assist Cloud, because I want to support them, every feature is available if I wanted to self host it. I freaking love them.
The only exception being Bitwarden, although they have paywalled features in their selfhosted builds I don't know of a better-for-me alternative. I could self-host Vaultwarden, but I pay for their subscription just because I want to support them.
My point is, if it's justified, I'll pay. Otherwise, I'll keep using standalone RSS apps on my devices and just backup my OPML every once in a while.
Is the selfhosted version able to also take email newsletters? I hate them and I'm using https://kill-the-newsletter.com/ to turn them into RSS, but I wish I had an all in one solution.
By supporting WebDav your app will instantly gain the possibility to sync with every OS and a gazillion apps. It is not the best protocol, but it's everywhere and it's very good when implemented well. For example, CopyParty's WebDav implementation is blazing fast.
Afterwards, you could enhance the experience by supporting websockets so that contributors can build clients specific to your project. This will take much more time to reach the user with a usable sync app, but can potentially end up in a superior experience.
I've tried several WebDav clients, and I've found that the great majority will work great. Their performance will depend on the server. For example, Nextcloud was slow. CopyParty was blazing fast, as if it was a local folder.
You might want to checkout CopyParty too, it's UX/UI sucks, but you don't need to see it, since you can use it with almost any client on any platform via any protocol.
TeamSpeek or Mumble.
Both have excellent voice chat.