The big problem with dual keyboard setups is, if the lower keyboard (usually the piano) has a ton of controls and displays on it, you can’t get the manuals close enough to move easily from one to the other, like you can on a B3 for instance.

The only way something like this would work for me is to get a dumb 88 controller with the best action possible, and sit the main keyboard completely on top of it, so the actions are close together and lined up.