Given that the D4 is @ $6k (pre-orders/RRP), I'd be surprised if canon doesn't drop the price from the expected 6800
At this moment, the the D4 appears to have a few obvious advantages over the 1Dx...
- video (uncompressed HDMI output)
- video (1.5 & 2.7 crop for 1080p)
- photography (F8 cross sensors)
- wireless work (with accessory - http://www.youtube.com/watch?feature=player_embedded&v=d0DnEoqm-wc
Potentially you could make a case for the XQD cards as well though that is neither here or there atm.
AF is also an area where canon could potentially lose out (based in previous history)
For certain people these differences would be sufficient to either tempt or convince them to switch - canon would certainly know that. An $800 price difference would make it a a lot easier for those tempted to actually take the jump as the cost of switching glassware is effectively reduced.
Imo, canon made a mistake with the long lead-time announcement of the 1Dx - given the only reviews have been with 'pre-production models' that are subject to change there isn't actually that much known about the camera (spec sheet stuff aside).
In contrast, following D4 announcement there have been numerous reviews/reports/you tube clips etc from people who have actually had a thorough play with the camera (as an example - http://www.youtube.com/watch?feature=player_embedded&v=jT0Pb5SNXmU
- long but quite informative). Thats what generates the hype/public interest
For canon people however, we have to sit and wait until the march release to get the equivalent info (i.e. post D4 release) - by which time you'll have had a few weeks of hands on D4 unboxing/reviews drowning blog and youtube sites