It seems that comments have the potential to be very powerful in providing real-time feedback to plugins to do a variety of things. However, all traditional comments starting with
; currently get stripped in the comm layer. To overcome this with the CancelObject plugin I was parsing file on upload to replace needed comments with another tag that the plugin could catch, do something, and then remove from the queue. This is non-ideal because now that gcode file is "tainted" with a non-standard tag. If this gcode is moved to another printer/octoprint instance there maybe issues if that tag gets passed to the printer. These tags could all be reverted on finish/fail/etc., (something I'm planning on doing), but that doesn't seem to be a particularly robust way of doing things.
My proposal would be to include a functional comment that would be allowed to pass through comm, something like
;# that would still always be interpreted as a comment by printer firmwares, but could provide useful information for plugins.