As for question 1, they're far more common in server grade stuff where typically they are baked in. Consumer stuff just doesn't need/use as much IO throughput and muxing that the FPGA provides on say, a large networking switch.

There are PCIe compatible FPGAs that you can plug into your desktop like a graphics card to accelerate certain tasks. In general though, our workstation hardware just isn't specialized enough to require them, but can be extended to do so. If something is a large enough business model, they'll just make an ASIC.