The way for new features like this to make it into the marlinbuilder would be with an issue there, and a pull request. I think that we will drag our feet more on new features first, preferring changes that make things more robust.
This particular feature does have a down side, which is that it will be a bit of a surprise to someone who is familiar with Marlin for 3D printing.
If this is set to 3000, and VARIABLE is off, what happens when the gcode explicitly sets the feedrate on a G0?