Variable Spot Colors from Illustrator Definable in InDesign
The ability to create a vector graphic in Illustrator, fill it with a variable spot color swatch (ie "Variable Color 1/2/3" etc.) and then when that spot color is imported into InDesign you can define it to match your project. Ideally on a per-instance basis, but even just editing the color globally from the swatches panel would be a big help. It would save hiving to make multiple versions of a graphic for each color you need - and that you may never need again.
For now my workaround is to make a layered PDF from Illustrator with a layer for each color and then turn on/off the various layers in the links panel, but not quite as effective as a variable color and gets tricky when the layers get complex.