About Discourse software... it's awesome. The ability to easily typeset code fragments, get nice previews with only a URL, and many other things is great. Any programmer forum should use it.
The only thing I can think of right now is the 20 character limit for a post. I assume it's mainly there to filter out a +1 or a Thanks, since that functionality is provided by the Like button under a post. I like the like button, it aggregates all the small posts in a single place and keeps the thread clean. Yet sometimes I see people still (need to) bypass the 20 character limit.
For example, if a post consists of multiple (possibly completely different) parts, and you think it's an addition to the discussion by letting people know you agree with one such part, how would you do so? Using the Like button you cannot differentiate between the parts.
This may be personal, but sometimes I feel that taking the time to reply, even if it's a simple 'Thank you!' is more of a thanks than simply hitting a Like button, for example if someone took the time to help you with a problem in a back and forth of a few lengthy posts.
Simply removing the limit will likely mean an increase in 'spam' posts, which is probably not desirable. Instead of blocking the ability to post, perhaps use some form of confirmation, along the lines of "Your reply has less than 20 characters. If it is a simple +1 or a thank you, the Like button might be better suited. Are you sure you want to post your reply?"
Hopefully something like that can still keep the threads clean and focused on a discussion, rather than one word replies, while allowing for a short reply in the rare case that it is useful (without using fillers that distract from discussion).