Thank you all for the comments!
Since concerns have been raised that another error reporting system may quickly go out of control, we've decided to not pursue this solution any further. Instead, we will try to rely on existing ftrace mechanisms to deliver notifications to the userspace, and perform dmesg collection/parsing once a notification is received. As a result, we won't need the error_report_start tracepoint anytime soon (I didn't rename error_report_end to something like error_report anticipating that error_report_start may be needed in the future). I've also dropped the error_report_notify library and the corresponding documentation from the patchset.
