A taller 3D printer would be great, that is a major reason why I got the Snapmaker. I bought into the idea of expanding it. It would also be nice to have a CNC side to the Snapmaker that can work on aluminum.
Other than those two things, one idea would be to create a rotating axis using one of the Z ports. That would open up the Snapmaker to a whole different ball game of possibilities. So it would be either a 3 or 4 axis CNC, depending on layout. If the rotating Z axis is parallel to the X axis, you would only need a Y axis to change height (creating a lathe). If the rotating Z axis is perpendicular to the X axis, you would nee another Z axis and a Y axis and now have a 4 axis machine. Not sure if this is even possible with the Snapmaker though, as I do not know if the double Z ports are just duplicates.
One more idea: combine the double Z, the stronger CNC and larger 3D printer. Large print bed supported by two Y axis motors. Have a splitter than just gives the same command to both, print bed keeps them in the same position. Double Z axis supports, with this using the extra long extrusions. Base of the printer could be the same idea as the stronger CNC, a frame instead of plate. There are 3D printers that function like this, but they don’t also do CNC and laser.