Re:
You could swap m900 and similar era Shimano shifters around or find aftermarket mounts for just the shifter pods, but I doubt anything newer would work as the design of the shifters and mounts changed. With the m900 style, the shifter pod was essentially a separate piece that could be bolted on, these days the upper part is a cover designed specifically to fit to the lower, so not even modern parts are that interchangeable.
Where there's a will there's a way, but not sure how strong willed you would have to be to make this work.