Not really a whole lot. FPGAs work best where you have precise timing requirements or really wide signals.
Most game engines are about throughput and I don't think you'd see a lot of use for them, heck we had a hard enough time using the PS3 back when I was in the industry and that wasn't nearly as wide as a FPGA can be.
Yeah, I was going to mention the PS3 too. It was the most unique hardware of the generation and definitely took the longest for devs to adjust to and learn to leverage fully.
Most game engines are about throughput and I don't think you'd see a lot of use for them, heck we had a hard enough time using the PS3 back when I was in the industry and that wasn't nearly as wide as a FPGA can be.