FreaknSweet

That's true, you can definitely make it more complicated, but I wouldn't expect a layer change within a layer, I'd expect the whole layer to be changed to the specified height. Understandably, with top/bottom at different layers, this would produce multiple layer height changes within the model, and maybe that would lead to more confusion then its worth. But, doesn't cura already do some more complicated layer changes with the Adaptive Layers option, although its only applied when certain conditions are met and can't be manually set.

Hmm, I had basically the same question with a different use case. I stepped up a few prints with a 1.0 mm nozzle, which is great for printing walls at 0.8 layer height, but the top/bottom get a bit thick. It would be nice to be able to thing them out a bit by using smaller layers. Cura currently has an option to have the initial layer a different height then the rest, so it doesn't seem to far off to have an option to setting the top/bottom to a different layer.