That's not deep packet inspection, just FYI. Timing and traffic correlation attacks never get any access to the packet information and piggy back on existing network weaknesses (correlating IP addresses based on timing metadata)
Yeah, but there's no need of "knowing all the variables in the system" and there's no "last time something like that was possible", it's always been possible.
And you get the "packet information" out of the exit nodes...
DPI usually refers to actually poking around the contents of the packets, which in TOR are (hopefully) minimally informative. With timing attacks you just keep track of the volume.
