Maybe someday AMD will release enough information about ATi's cards that the open-source drivers will become as reliable and featureful as Intel's...
Are you referring to the fact that NVIDIA's drivers aren't open-source? Well, there is no reason to expect that Larrabee's would have been.
In any case, there is probably nothing interesting in the driver source code anyway. (A lot of "copy this buffer of instructions to the GPU, this buffer back" and not much else.)
Also, apart from the Paulsbro/GMA500 fiasco (which was contracted out to a third party), all Intel's graphics hardware has had open-source drivers written by Intel themselves, so it doesn't seem too extreme to expect similar support for Larrabee.
You have a point, but I think the reason NVIDIA doesn't open-source the drivers is the same as the reason Larrabee probably wouldn't open-source them - i.e. fear of releasing the details of the GPU design to the competition. Current Intel's graphics has nothing to hide from NVIDIA, but Lrrabee would. But of course, this is just speculation, especially now that no consumer Larrabee is on the horizon...