Nice. So I guess the business model is now purely about hosting the central servers for everyone? I'm fine with that, I hope it works out for them. I've been a satisfied Threema user for years. The main problem, as with all messenger systems, is network effects.
The less optimistic views are that (a) this will destroy their business since people will manage to write self-hosted servers that make Threema's hosting services redundant, or (b) that they know that their business is on the way out, and this is giving back to the community before they fold. I hope that's not the case.
Open sourcing the apps doesn't make them free in the app stores. But it means that anyone can publish a build for free, no? Either on GitHub or wherever, for people who can install an APK on their device. Or in the app store, as a rival "free Threema clone" or whatever (I guess one would have to be careful about trademark issues).
If you want to be in the official network, yes. But like I said, open sourcing the client possibly open sources the relevant parts of the protocol that would allow compatible, maybe even federated, self-hostable and free servers.
The less optimistic views are that (a) this will destroy their business since people will manage to write self-hosted servers that make Threema's hosting services redundant, or (b) that they know that their business is on the way out, and this is giving back to the community before they fold. I hope that's not the case.