I have completed work on confining Syncthing in SELinux and my pull request is avalable here:
The downstream distributions will need to pull from upstream and adapt to suit their needs. Fedora/RHEL will need a little bit of extra work due to their use of the config_home_t type. I’ll be happy to help port, but I’d need the distributions to want to help port in the first place 
Lemme know if you have any questions, please contact Fedora/RHEL and Gentoo to get the changes pushed downstream 