a few 360 questions..

[wolfy]

Is Jtagging as futureproof as possible?
Is any 360 Jtaggable even if it has already been chipped/flashed?

[Acheron]

Jtagging gives you the option of playing homebrew/DLC. You still need to flash or chip (no point in chipping though) your 360 to play backups.

Previous flashing has no effect on Jtagging but I am not sure if they ever worked around Jtagging units that had their kernel updated beyond a certain point.