[css-color-5] in <space> syntax for linear-gradient() et al #6667

The nice thing about color-mix() is that it allows you to specify colors in a different color space then the color space in which the interpolation happens. As far as I can tell, linear-gradient() et al will always interpolate in RGB space, and I can’t find any changes to linear-gradient in CSS Color 4 or 5. Would it be feasible to add a in <space> syntax to linear-gradient(), similar to what color-mix() supports?

Here’s what gradients from blue to green would look like (I used JavaScript to generate these gradients using color-mix()):

cc @argyleink