Does magic lantern stay on the cf card?
Yes it does, so if you put in another card ml is is gone. Just be sure never to use a cf/sd card with the bootableflag set in firmware & on the card (eos utility) *w/o* the ml files or the body will lock up.
Any idea if a version supporting the 1DX will ever surface?
No dual cpu bodies run magic lantern (7d, 1d series), afaik no work is done on the 7d anymore to get around the problem of being unable to run user code and for 1-series development you'd have to have devs with access to the body and willing to brick it. But I'm happy to stand corrected if anyone knows more than what is available on the ml site and in the forums.
already got enough funding and has purchased a 5D3 body, development will start soon.
I did all the initial testing with Alex since March when 5D3 was released and took that "Hello World" photo, I bricked my 5D3 numerous times and all successfully unbricked. The latest build I tested works really well considering it's done in just a few months, I believe it definately won't take a year from now for a stable 5D3 release.
In this case, please update the ml website or at least the forum and let people know :-o ... and I admit my first "a year until 5d3 port" prognosis was half a year ago, so maybe I'd adjust that when repeating it :-p
