Just a guess, but they project the cost of large scale GPU manufacturing to decline faster than ASIC due to the shared applications of gaming/VR?
Edit: going with GPUs makes sense now, but it doesn't indicate a big bet on Facebook's part. I don't think opensourcing a server cabinet is that interesting, but I'm a hardware engineer.
In 10 years I think more people will touch AI than VR but I don't know how that translates to investment.
AI is nowhere close to strong AI or reasonable general-purpose intelligent programs that don't require loads of human tuning. It will take several breakthroughs.