[g-b-r]

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...

[roywiggins]

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.

[g-b-r]

Why is DPI still being brought up? And what was wrong in my message?

With timing you keep track of the volume and... timing, which (often) allows you to correlate the entering and exiting traffic...