I've had an idea :-D
The C64 DTV chip on a PCI card with a TV Card-like application running on the Workbench to display the video output in a window. When the window is selected, the software routes keyboard and joystick input to the PCI card, which in turn routes these inputs to the DTV chip.
It's a C64 on a PCI card! :-) :-) :-) :-) :-)