Hold off on the 1DX. The 5DIII comes very close to 1DX performance and in some aspects is better. Both have their advantages but if you have the 5DIII then it's likely a waste to get a 1DX unless you need the 1DX features for sports photography. Wait and see how the 7DII comes in.
If you are itching for some new glass, then trade in the 500 F4 IS and get the 500 F4 IS II. The lighter weight, improved IS and improved IQ is worth spending the money on.
I am considering an upgrade to my equipment
1D M4 -> 1Dx
500F4 IS -> mark 2 version of this lens
Already have the 5DM3 but love the feel of the 1D series, though it is a lot of $ for a body.
Mostly shoot wildlife with the 1D and use the 5D for macro and scenics (the tiny bit I do of city scapes).
Really don't need any new lenses - in fact, I need to have a garage sale and join a 12 step program for lenses and bags.
Originally I was very skepical about the 1Dx but the more I hear about it, the more I am interested. I will be borrowing one for a shoot next week, so I will have hands on experience then.
I could also wait, to see what Canon introduces this fall.
High MP camera (probably a replacement for the 5DM3, not sure if it would be wildlife camera)
200-400 zoom in lieu of long lens
Did you not answer your own ? by saying you already have enough lenses?