The first thing is that not only is the sensor in the 1D X larger (full frame, like the 5D, rather than APS-H or 1.3x like previous models) but the megapixel count has dropped from 21MP to 18MP. This is a fairly ballsy move by Canon and shows they've recognised that actually resolution isn't the be-all and end-all of image quality - noise is just as important. This means the pixels are larger and can collect more light, so low-light and noise performance increases. This is particularly good for video, where noise is much more evident in a 1080p 2MP frame than in an 18MP photo.
The second significant upgrade for video is a huge increase in processing power (the new Digic 5+ processors are apparently 17x faster than the old Digic 4). We won't really see what this means until some video samples are released and there are some more hands-on reviews, but it bodes well for things like line-skipping/moiré, HD out while recording and being hackable to faster frame rates and higher bitrates with tools like Magic Lantern.
Finally, a new recording format with substantially lower compression plus the ability to record for up to 30 minutes is going to be beneficial to both people using them on higher-end productions (particularly when used as a B/C cam alongside an Alexa/RED) and those working in documentary/live event type work.
What this means for the 5D Mk. III is a tricky one… it's got much more name recognition than the 1D and is in the right kind of price bracket for pros and keen amateurs alike, so it would be daft for Canon to leave out too many of these features, but I wouldn't necessarily put it past them. Either way, they certainly seem to be listening to the DSLR community and what with these updates and some far from perfect products by other manufacturers (see Panasonic AF-100 and Sony FS100), it would seem the video DSLR isn't quite dead yet.