Is the client the important part of the software, or is there a server side?
That said, I'd like to open source a server. We need a reference implementation of our control protocol so it can be properly analyzed by security experts. Not sure what form that should take yet, but I'd like it to be usable.
Your coordination server tells every node about every other node and distributes the keys for the entire network. Everything on a tailscale network implicitly trusts your coordination service.
If an individual client is compromised, code or otherwise, the effect is more limited than your coordination service being compromised, in which case the entire system's trust is broken.