One thing to consider is going from APS-C to Full Frame with regards to your focal lengths. It's a lot easier to go wider on full frame, but it's harder and more costly to go longer. If 200mm on APS-C was about "right" for you, and you were always at the end of the long side of the focal length of your 70-200, on a full frame, you'll be really struggling for reach, so you will lose significant pixel density on your subjects. This is something to consider. If you were often on the wide end, then maybe this isn't a problem.
Personally I went from a 7D to a full frame 1D series for lots of things, and eventually went back to a crop for my action/birds/wildlife because I preferred the combination of smaller, faster, lighter glass with a crop, than dealing with a full frame and a huge long piece of glass. Just my preference. So I keep a small full frame (5D series) for portrait and stuff, general day to day shooting. And I use my 1D crop for birds/wildlife/action. The pixel density difference was enough that I sold my full frame 1D, and went back to a crop 1D.
The 1DX is a great camera for action and low light shooting. Can't go wrong with it. It's still a little expensive I think on the used market ($2.5kish). Mean while, for that price, you could get a 1DIV ($1kish) or 7D2 or 80D (less than $1k) and a 6D ($850ish) for less than that cost of a 1DX and have an action setup and a full frame setup for portrait/landscape and two cameras.