I do medical journals, and I frequently have clients who request their document in 2 versions: a full color version for online, and a version where some, but not all of the pages are in grayscale for the printer, to save on printing cost.

It is yes possible to export an entire document converted to a grayscale color space, with some admittedly janky workarounds which it would also be nice to see streamlined.

But at the moment, what I do for my needs is I have to export a full color version, a separate grayscale version, and then manually collate these together in Acrobat to get the desired PDF. Being able to do this in one step exporting from InDesign would be great. Especially for those of us where manually creating a separate InDesign document devoid of color in some places, when there are sometimes hundreds of figure images, would be very time consuming.