I would love to add it to my 1Ds3. I recall reading that once upon a time Canon wrote ML devs a strongly worded letter telling them not to touch a 1D, but a camera that old is long obsolete.
(I literally only want a raw histogram)
(I also have a 1Dx2 but that's probably a harder port)
I have been toying with the idea of picking up an old 1D. I can't remember the guy's name that I saw do this, but he had his 1D modified to use a PL mount instead of an EF mount. Something about the 1D body (being thicker I guess) allowed for the flange distances to work out. He then mounted a $35,000 17mm wide angle to it. That lens was huge and could just suck in photons. With that lens, he could expose the night sky in 1/3 second exposures what would take multiple seconds on my gear. He mounted the camera to the front of his boat floating down river using night vision goggles to see where he was going. The images were fantastic. I always wanted to do something crazy like that
Canon have never had any contact with ML project for any reason, to the best of my knowledge. The decision to stay away from 1D series was made by ML team, I would say out of an abundance of caution to try not to annoy them.
Might be time to reconsider. Canon are (supposedly) not planning any further flagship DSLRs and I see little wrong with modifying your own property.
Independent of that: how dangerous is ML dev to the cameras themselves (in terms of brick potential)? Permanently bricking a camera in the price range of the 1DX is not exactly my idea of a good time. :-)
Over the years, a few devs have temp soft bricked cams, requiring various non-standard methods to restore them to working order. I think all attempts succeeded so far! I don't think any permanent physical damage has been triggered by devs. It is definitely a real risk, but we try to work with the OS when possible, and the OS was written to try to make these things hard.
I don't think I'd want to learn the ropes on a cam too expensive to psychologically say goodbye to. Maybe save that for the second port.
Actually when I go back to the 1Ds3 from my 1Dx2 the only thing I miss is the front buttons near the lens mount, which I use for playback and magnification.
(I literally only want a raw histogram)
(I also have a 1Dx2 but that's probably a harder port)