Will it work on the 7D?
Short answer: Not yet. But work is being done on producing a Magic Lantern image for the 7D. Currently we can generate signed firmware images and have dumped the 7D's ROM for analysis. If someone donates a 1D Mark IV, I suspect the same techniques will work to produce a version of Magic Lantern for it.
While we can generate signed firmwares, we're not able to cause a clean reboot to start our process with the RAM copy of the ROM startup code. We can't even jump back into the ROM, so at this point we're not able to run our own process alongside the main firmware image.
....shitty.