Switching between water based paint and solvent based paint requires a lot more changes then just guns. It requires a different cure setup, booth filters are slightly different your booth air temps, humidity levels all change. As for two guns, I have never heard of two separate guns on the end arm of a robot like the 50ib. Really the only thing different for a solvent based gun and a waterborne based gun is stainless steel fluid passages. Waterborne paint is abrasive and will over a few weeks eat out the insides of guns intended for solvent based paint.
With a gun that has all stainless steel fluid passages you can run solvent based and waterborne paint through the same gun. All you need is a color change dosing system. This would enable you to switch color or type of paint.
They also make end of arm quick change guns. The gun mounts to a block with a turn of a lever. to swap out guns purge, after purge cycle flip lever remove gun put on different one and color change and away you go with waterborne paint. If you wanted to go in that direction.