One addition. In this guide Use a subfolder (path prefix) to serve Discourse with multiple servers sharing a domain it says that
Note: This won’t work for serving multiple Discourse instances from different folders on the same domain. You need to use different subdomains so that each site can have different cookies.
So with this change you could remove that note. There’s no need for different subdomain if the cookies are scoped by the path. Or are there any other reasons why one couldn’t host two Discourse instances from different folders?