[pclmulqdq]

Intel at one point tried an FPGA-in-package with a server CPU. It turns out that you can't downclock/power gate parts of FPGA designs nearly as easily as you can CPU components, so the whole package had thermal regulation issues. You had to run the CPU at a very conservative frequency in order to let the FPGA use power as it needs to.

There are FPGA-SoCs out there that are mostly FPGA, and that seems like the way to go if you want to combine FPGAs and CPUs, otherwise they should probably be on separate power and heat budgets.