Not a language proposal/idea. GitHub has just made its Discussions beta generally available, and it's a good fit for this forum. Some reasons:
- One less login for everyone to remember/worry about
- Lower barrier to entry to find, create and react to proposals*
- Better cross-linking integration with ideas that eventually become their own proposal repos
- Better cross-linking integration with issues/pull requests in other GitHub repos
- Easier to configure email notifications, watch topics etc. I sometimes miss messages here.
- (probably) easier for admins to manage access control
*could be a double-edged sword, but it'll give better signals by way of 
/ 
votes at least since not many people will sign up for discourse just to give a thumbs-up
Example forum: https://github.com/vercel/vercel/discussions