This is somewhat incorrect. The interlaced copy modes can do what you're looking for, and were used by Swiss in the past.
This is essentially the method currently used by Swiss, but without using the vertical filter to do 2:1 linear downsampling.
Update: I made a modification to libSDL2 to use embedded-game-controller (and therefore bt-embedded) as the input backend. This is currently waiting for review (fingers crossed!).
I made a new release of the VVVVVV game using this library, and...