The Tech Report had a chat with Raja Koduri, AMD's head of graphics hardware and software development, and got to hear that frame delivery issues on systems that use CrossFire in combination with Eyefinity or 4K will be resolved later this fall via a driver fix:
In our talk, Koduri acknowledged that the frame delivery issues with CrossFire were "unfortunate," and he expressed a desire to make things right. Koduri told me AMD is working on a fix for CrossFire and single-large-surface display configurations, like Eyefinity and tiled 4K monitors, for current Radeon graphics cards. He said AMD plans to deliver a driver with the fix this fall.
AMD's newest Radeon GPU, the "Hawaii" chip that will power the Radeon R9 290 and 290X cards announced earlier today, will of course be a top priority, as well. Although we can't yet divulge too many details, we expect Hawaii-based graphics cards to arrive with a very capable solution for CrossFire frame compositing and pacing already in place.