I would add some of the self-hosting solutions, which are already used by eager adopters of decentralized solutions, e.g. nextcloud.com, yunohost.org and freedombox.org.
The main question for self-hosting is of course which server implementation to use. And if there might be a dependency on Apache, which still breaks RS servers. Also, if there’s a central user management system, then it would be useful to have the auth be pluggable in the RS server that’s being used, of course.
True! I’m excited about renewed activity around Armadietto in this regard! Considering that JS is basically the most widely used language atm, it will probably end up being the most active server project.
But also php-remote-storage is still the most mature solution I think, and should be especially easy to deploy when the latest Apache release (which contains the important bugfix for RS) is available in package managers. Furthermore, considering the ever-growing popularity of Rust, we do still have mysteryshack available, which is also a working implementation, and could be picked up by a new maintainer at some point, too.
In general, however, I think it’s still difficult to plan for mass adoption, because the protocol is still an Internet Draft at IETF. So a company-driven solution like e.g. nextCloud is not a good target yet, because the company would have to support potential radical changes to the RS integration, which could happen anytime until the spec is an RFC.
P.S.: People can also still be paid by Digital Ocean for writing tutorials on setting up server software. Would obviously be useful to have some guides for RS servers over there…