FPGAs are not power efficient at all vs GPUs and ASICs anyway, which is going to be especially true when they are fully saturated by LLM inference.

That said, FPGA do provide a middle ground, but using it for speed and power efficient is not a forte, and the true value exactly comes from this focus alone: it allows you do emulate systhesis and verify that your logic is correct before you do full ASIC tapeout, e.g. building softcores for CPU validation

Anything else is added and unintentional benefits.