But no, imho blockchain isn't the future of everything, it's a solution for handful of things, and in majority of cases blockchain apps are just a bulky & unnecessarily costly alternative.
I mean give me one example where centralized solutions, like open sourced and private Signal wouldn't be a better choice and easier to adopt for messaging?
If argument is privacy, then most blockchains aren't even private in their core level like signal. If the issue is censorship, then i would like to know who has been censored and by whom. And reason why exactly is that a bad thing?
Signal may be open source, but the company still runs its servers (infrastructure). Doesn't that make it centralized? I understand Blockchain can't be used for everything, but I don't think IM will be much of a burden to it. Especially if messaging apps are built on a separate chain (L2 or sidechain). They will only obtain the main chain's security benefits. The rest will be handled off-chain by a L2 or separate scaling solution.
By the way, I've forgot to include David Chaum's xx messenger (powered by the xx network) on the Blockchain-based messaging app list. It seems to be a far better solution than others. The main selling points of such messaging apps are privacy and censorship-resistance. You will truly own your data without having to worry about governments or third-parties getting their noses on your private business. It's much harder to compromise a Blockchain-powered messaging protocol, than a standalone (off-chain) alternative. Especially centralized software managed by corporations. They can install an undetectable backdoor that will grant the government access to your conversations. It's also possible to seize centralized servers (or shut them down) just to prevent people from using the messaging app.
There hasn't been any case of censorship on Signal (yet). But that doesn't mean it's trustworthy. If you can't run your own servers, it's not safe. Time will tell us if Blockchain-powered instant messaging will become a failed experiment or a huge success. I'll pay close attention to development updates.