That's https://github.com/tailscale/tailscale/issues/1572 which we haven't given up on. It's just not done. We did it for macOS and we thought the same thing would've worked for iOS (they share ton of the same code) but it apparently didn't work.
The mobile apps have been a low priority thus far. We just recently hired some people to work on them, though.
The highest priority for them currently is fixing battery life (we do some dumb things when LTE + wifi are both available, and when using exit nodes, and some unnecessary heart beating that sucks on mobile) and then there's also a mobile app redesign (or just "design" coming).
We like Headscale and we're super glad that it exists. (they saved us some work by doing it first, as our control server wasn't in a releasable state) We keep Juan et al updated when there's protocol changes or things they can do. (e.g. recent https://github.com/juanfont/headscale/issues/552)