U.K’s Retro Gaming Cables is now selling a bare-bones board that essentially takes RGB in through Scart and outputs the signal through BNC: https://bit.ly/2OgZif3
It also offers a sync stripping (using the LM1881 chip) option that can be toggled on or off. Audio is also conveniently extracted from the Scart source.
As this is a board-only product, all the other peripherals required to make this a fully-working unit, are to be provided (and assembled) by the end user
I’m sure this will come in handy for many different setups so grab it if you need it!