FB-DIMM is for servers only. Why would you want fully buffered ram in your PC ? Also FB-DIMM has HUGE latencies, but can draw 17GB/s BW with quad channel.
This agreement between AMD and RAMBUS was signed way back in past - we had thread about that here And since RAMBUS has the Rights to everything that`s intersections with DDR ANY company that wanna use them MUST have an agreement with RAMBUS.