[cormacrelf]

Yes, at the limit (not sure if US laws have caught up to Australian ones in this regard) they could potentially be forced to push an app update to carbon-copy all messages from specific people at the client side, unencrypted, to the government. This is generally why people care about having the app available on F-Droid, because you can more easily analyse DIY "supply chain security" on your own copy of the app. The other solution is what Matrix does, which is to encourage people to develop many different client implementations.