To discuss SMuFL with other developers and interested parties, please join the W3C Music Notation Community Group. Once you are a member of the CG, you can post to the public-music-notation-contrib mailing list, to which you are automatically subscribed when you join the CG.
Current discussion on public-music-notation-contrib
You can read past discussion in the list archives.
Past discussion on SMuFL-discuss
Before SMuFL development moved to the W3C Music Notation Community Group, discussion took place on the SMuFL-discuss mailing list. You can read past discussion on the SMuFL-discuss mailing list via Nabble.