Would having multiple servers help here, anyway? Once your data leaves your own server, you would then be in untrusted territory assuming the server needed to be trusted.
Basically the same threat model the Signal people themselves address when talking about court orders and subpoeanas received by their corporation for "customer" data.
> Does Signal send my number to my contacts? Signal does not send your phone number to anyone unless you send them a message or make a call to them. The Signal service does not have any knowledge of your contacts. Data is all owned by your phone. Registration notifications are never transmitted by anyone in any direction at all; these notifications are created by your phone.
> How does Signal know my contact is using Signal? Signal periodically sends truncated cryptographically hashed phone numbers for contact discovery. Names are never transmitted, and the information is not stored on the servers. The server responds with the contacts that are Signal users and then immediately discards this information. Your phone now knows which of your contacts is a Signal user and notifies you if your contact just started using Signal.
https://support.signal.org/hc/en-us/articles/360007061452-Do...
(Btw, I think that first sentence is a bit confusing and should be classified/reworded.)
These would be equivalent to phone numbers, for all intents and purposes. The number space is trivially small.
This kind of obscurity makes it unnecessarily hard to understand what the argument really is.