Kbin is very young, so the documentation is lacking basically everywhere. The developer, ernest, was scrambling this weekend to get some of the docs around setting up a server in shape for tomorrow, and desperately trying to keep k-soc's hamster alive as the instance went from a few dozen to several thousand active users.
Ultimately, despite its level of polish, it's not production level software, and we're all just making due.
The project is open source, though, and there's nothing stopping anyone from making mobile apps are alternative web front-ends. By the end of this week, there will likely be dozens of servers running kbin, if not hundreds, and whether they want to allow external actors to use the API will be up to each server's administrator.
But anyone thinking about it should be aware that ernest was contemplating making the kbin API Lemmy-like, as Lemmy has a significant head start on number of sites running it, and until very recently number of active users. But given the explosion in attention kbin has gotten, and the explosion in population on k-soc, that might not be a priority any longer.