Oil splatter may become more of a nuisance for landscape and portrait photographers. But then again, the 1DX, while capable of capturing great landscapes and portraits, was geared more towards sports/action, which more often requires shooting at high iso and wide-open apertures. The one exception that I can think of is if you're shooting airshows trying to capture propeller planes and helicopter blades.
I'm sure there may be a handful of other exceptions but I can't think of them at this time.
So I would say most of the time, the oil splatter isn't going to be that big of a deal. But for those who aren't comfortable cleaning their own sensors and/or often shooting with aperture closed down, I can see this as a thorn in their sides.