That makes sense and seems like a legitimate line to draw. Being a little bit of a pain, I would point out that the Google Play store and Google's components for Android are not open source. If you're willing to make Tailscale available via Google Play, and open source the client, maybe iOS can as well? And while we're at it, macOS apps can be installed out of band of an app store, so maybe that can be open, too. It could even share a codebase these days.
I'm not a Tailscale employee, but Tailscale works on FireTV, so it is clearly not reliant on Google-provided services. They also provide a build for F-droid from the same code base that doesn't use any external services. https://github.com/tailscale/tailscale-android/blob/main/and...
As far as I can tell, the only Google Play Services API the app distributed on the Play Store uses is Google account authentication via the Play Services Google account picker.
(Personal opinion here) Keep in mind that we're still a relatively small (but growing) team, and I think that a big part of not open sourcing everything is a simple matter of having the capacity to properly engage with the community.
For now, we've optimized for doing that for operating systems where users most expect it.
In general the OSS operating systems get OSS clients, whereas the closed-source ones don’t necessarily get the full OSS treatment.