So the Architectures of the last 4 supercomputers might be surprising.

x86-64 with Radeon
Arm and something else.
Power9 (2 Processors paired with 4 Tesla GPUs)
Sunway

PowerPC is not dead and Sunway is believed to be most closely related to DEC but that's a stretch.

PowerPC, OpenSPARC and other open RISC designs aren't going away anytime soon.