Given that happened six years ago and multiple unofficial clients continue to exist without threat of ban, I'd suggest this one example cannot be extrapolated.
It is true that Whisper Systems runs the network and can gatekeep it as they see fit.
But your claim that Signal, as a matter of course, bans unofficial clients is objectively not true.
Moxie has been pretty consistent on this point. He even gave a talk at C3 a couple years ago that was basically an hour long explanation for why he continued to think this way and that he hadn't changed his mind at all. https://media.ccc.de/v/36c3-11086-the_ecosystem_is_moving
Additionally, they're more or less required to go after trademark violations if they get too big.
> He even gave a talk at C3 a couple years ago that was basically an hour long explanation for why he continued to think this way and that he hadn't changed his mind at all.
In that talk he explains why they don't decentralize their protocol or the ecosystem.
His concern is that a decentralized ecosystem means actively supporting third party implementations and having to achieve consensus when making changes, which slows down (or flat out stops) their ability to evolve the protocol and turn out new features.
That's a totally orthogonal issue to banning unofficial, unsupported clients.
> Additionally, they're more or less required to go after trademark violations if they get too big.
That's a trivial problem to solve: don't put Signal in your client name.
The unofficial clients are part of the ecosystem. Centralizing the ecosystem means centralizing the back ends and the clients.
It's not orthogonal at all, and he's talked at length about how he views every client connected to their servers as under his control, and his dislike for unofficial clients, and his willingness to squash them if they get too big.
Before signal he was head of security at Twitter which has a similar 'squash unofficial clients if they get too big' policy.
> That's a trivial problem to solve: don't put Signal in your client name.
Unless there’s an official statement about unofficial clients being allowed, then that single example can and must be extrapolated: it’s the only factual evidence.
It is true that Whisper Systems runs the network and can gatekeep it as they see fit.
But your claim that Signal, as a matter of course, bans unofficial clients is objectively not true.