From a technology perspective, Intel and Mobileye are both bringing experience in machine learning and computer technology; Intel's been working on autonomous driving tech for several years now. Ultimately, the companies all want to push driverless cars forward to the point where they reach the "eyes off" and "mind off" stage of the game, where passengers aren't required to keep their hands on the wheel, eyes on the road or any of the other things we take as part of the current driving experience.
All three companies have agreed to "deliverables and milestones" to reach that 2021 goal, but they aren't talking much about what those are just yet. In the short term, the partners will show off an autonomous test drive featuring a "highly automated driving" prototype. What exactly that means remains unclear, but it seems like we should see things come out of those partnership before too long -- by 2017, BWM, Intel and Mobileye want to have full fleets of vehicles performing "extended" autonomous test drives.