Around what time will Korean get out of Beta?
I can't answer your question in any authoritative way but I'm about 2/3 of the way through the tree and there are still many, many problems. I imagine they're still getting a lot of reports at the moment.
I commend the deveopers for the many corrections they have made (going through the course for the 2nd time I see lots of improvement) but hope it stays in Beta for quite a while, as so much more could be added, and there are still many corrections to be made and alternative translations to be allowed. I am hopeful https://www.duolingo.com/comment/25350572 will be successful in recruiting more help to provide for further devfelopment.