Nothing says "hacker culture" like voluntarily submitting your photo ID and a real-time facial scan to big brother so your de-anonymized communications can be permanently logged and used against you by the state as soon as a future administration decides you're a disfavored person.
IMO, Matrix is definitely the best protocol for sending oneself messages in a running thread across all of one's devices. That is one excellent use case, and it's a real one.
It is also great for the same thing, but with other users, too. I have no idea why its current uptake is so slow among small groups. Is it the apps? The fact that you need to find or join a host (or self host)? Merely being "one more app" and "unknown"?
I wonder what the Matrix team is doing to smooth out whatever adoption issues it has. I think it is worthy of more adoption.