I've taken the liberty of creating this wiki page:
https://github.com/oasis-tcs/sarif-spec/wiki/Notes-on-known-extensions-to-SARIF,-by-spec-areato try to organize known extensions to SARIF (e.g. property bags) by
specification area (rather than by producer), which might help identify
areas for future standardization.
Hopefully this seems useful.
I've populated it with the things GCC is doing in its SARIF; please go
ahead and add entries for things your producer is doing.
Dave