Are there any aircraft that come with interchangeable flightdecks? With the new Boeing 787 where Boeing has provided the capability to swap engine types if the aircraft goes to a new operator quite quickly, I'm wondering if there are any interchangeable flightdecks? 

Say that you might have a legacy 737 for southwest, but an entirely different cockpit layout (containing the same capabilities) for a company which operates Boeing 787s as well, since the similarities would make training easier.

I know a similar project was done on the DC-10s becoming MD-10s, as well as some Saudi MD-90s to be similar to MD-11, but both of these were long-time consuming projects. 

But I'm wondering if there are any aircraft which have this possibility and if not, why not? I'd see it as an opportunity to Boeing to have a 787 flightdeck shared with say the 777.
According to this answer they used to be very customizable, but not very much interchangeable at least to the point that no one bothered to change them on second-hand aircraft. They are reducing it because it only causes confusion. Aircraft change owners and pilots change employers and it's most useful if all aircraft of the same type have the same cockpit layout.

As far as 787 goes, it has very similar flight deck to 777, always, to the point it has common type rating.