The heart of the Spectrum Next is a Xilinx Spartan-6 XC6SLX16 FPGA (field-programmable gate array, magpi.cc/spartan6). FPGA isn’t emulation: the programmable logic blocks create a perfect representation of the Z80 chip.
You can take the FPGA beyond the Z80 with processor cores. We turned our ZX Spectrum Next into a BBC Micro B and BBC Master using BeebFPGA (magpi.cc/beebfpga). Victor Trucco has made a range of Intel 8080 cores available, including MSX, NES, and Colecovision.