Personally, I'd generalize the question to "Why not allow the customer to specify keycap type and case colour seperately?"
Maybe something like:
"Connector Type - USB / PS/2"
"Mechanism - Springs / Membrane"
"Case Colour - Black / White"
"Key Colour - White / Silver / Black with no lettering"
I wouldn't mind the white/tan keys from the white SpaceSaver on a black Customizer case, for example. (I'd swap with a 1391401, but they lack the right bottom row)
I think a good "Will this shut you up?" question would be if they could basically summarize what their facilities are capable of-- "We can't do A, B, C, or D because X, and we can't do E, F, G, and H because of Y, so stop asking!"