The Sony CXA1585Q chip converts Y/C to RGBS.
It needs external power and some supporting circuitry, and it has some tunable settings. I envision a small box with S-Video (in) and SCART (out) connectors, a micro-USB for power (and maybe a 2nd for daisy chaining power), and some small pots to adjust it specifically for the system you’re plugging into it (C64, GameCube, N64, etc.).
This would work well with SCART switches.