There is a relatively good Yoon-Suin community page on G+ which, aside from the blog, is the main place for discussing the setting online. There is lots of interesting stuff there. Clearly, that page will have to disappear when G+ goes away. I am currently considering options for replacements.
Please let me know in the comments to this entry (or on the post on G+ - I will cross-post this to the Yoon-Suin community page there) what your preferred option is:
a) A discussion forum on the Noisms Games website (yes, this exists!)
b) A subreddit, if this can be arranged
c) Something on MeWe (I don't have a MeWe account yet, but it seems to be where a lot of G+ exiles are heading)
d) Some other better option I've not thought of (and tell me what that is and why it's good!)
Please don't recommend anything to do with Facebook or Twitter; I don't use them and dont intend to start.