I'd consider end-to-end encryption to also be table-stakes, at least opportunistically after the first message in each direction. With encryption cached messages are far less harmful (though still leaking very useful metadata), without encryption it seems almost trivial to spy on any communications

> instead of just retrieving the messages from the cache on a confiscated phone

why wouldn't encryption be a part of recipe here rendering government acquisition of such a cache moot?

> The government would actually need to infiltrate the network in order to read the conversations

If I understand correctly, this would still be true if the recipient is connected.