Actually opening issues via email would be nice to. Trac isn't perfect, but I remember email2trac[1] quite fondly. Combined with email notifications on change, it made it easy to forward bug/error-reports to a trac instance, and automatically create an issue. Or just let support@ go straight to trac.
I still think having an email interface (as in: in addition to a REST API) is very useful. Having a web interface as well isn't bad either.
[1] https://oss.trac.surfsara.nl/email2trac