It's a good thought experiment. Let's assume signal is a conspiracy.
What do we do now?
The article doesn't seem to have any thesis here. If signal becomes untenable:
Briar and simple x are the most promising in my mind, but I know there's a lot of proponents of matrix.
I personally don't think session is sustainable, simply because they don't have any development going on, no perfect forward secrecy added.
If we're talking about the signal replacement, we need a way for people to find their contacts. A phone contact list as a social graph is pretty good. I could see that being added as a discovery, optional, service for simplex, or even briar. But that would probably take quite a bit of development of work to do it in a non-Spammy fashion