[pimterry]

The only risk is if you've served HTTPS traffic properly with HSTS headers to users, and then your server is later unable to correctly handle HTTPS traffic. Note that HSTS headers on a non-HTTPS response are ignored.

Whilst there's cases where you might fail to serve HTTPS traffic temporarily (i.e. if your cert expires and you don't handle it) almost all HTTPS problems are quick fixes, and are probably your #1 priority regardless of HSTS. If your HTTPS setup is broken and your application has any real security concerns at all then it's arguably better to be inaccessible, rather than quietly allow insecure traffic in the meantime, exposing all your users' traffic. I don't know many good reasons you'd suddenly want to go from HTTPS back to only supporting plain HTTP either. I just can't see any realistic scenarios where HSTS causes you extra problems.