Devs did give heads-up for custom client developers.Problem is that most players rely on public clients developed voluntarily. Factions literally tend to have their own in-house developer basically.
Technically, "private client" goes against the open-source licensing (or maybe this would just mean that if private client source code gets leaked, there's zero legal ground to sue people using the private client code for anything they want.) In any case, there are no Cyberpolice who can force people like Snail to share his toys.