Earlier quoted context omitted.
The problem with statements like "I happily use Matrix but my grandma will not, ever, not in this world" is that Matrix is more of a protocol than anything. So of course, your gradma would never use HTTP, but since browsers are now user friendly enough, everyone is using HTTP indirectly. Same can (will? Might?) happen with Matrix, where a popular applications get written on top of Matrix, and users don't even need to…
And when a popular application get written, it will become the next walled garden. whatsapp uses xmpp. whatsapp became a closed system. PerfectClientXInTheFuture uses matrix. PerfectClientXInTheFuture becomes a closed system. Why? Because that way they can make more money. It's sad, but true.
If we manage to keep the governance of the client and protocol open and participatory, I'm sure we can have clients/protocols that survive for longer. Just like we did with email and IRC in the past.