The Youtube algorithm just brought this awesome tech to my attention, and already I'm thinking about trying to build one :) Basically you use a relatively low pressure water jet (50-800bar according to Synova's site, as opposed to 2000-6000bar for regular waterjet cutting) to guide a laser by total internal reflection, giving a much finer and straighter cut than a laser in air. Plus the water clears away swarf and cools the surface to create a super clean cut with minimal heat-affected zone.
I don't know if there are any shops where I could send work to be cut on such a machine, but I'm sure it would be out of my price range anyway. But it sounds like the fundamental cost should be relatively low since there's basically no force involved so you can use 3D printer style motion system, and a cheap 200bar pressure washer pump should be good for the water jet. So the only really difficult task is making the pressure chamber and focusing system.
Has anyone heard of prior attempts to DIY, or have any interest in collaborating? It's surprisingly difficult to search for because all you get are comparisons between regular waterjet cutting and regular laser cutting. I have no experience with lasers, but I have designed and built a CNC mill and 3D printer, so I should have no trouble with the motion system, and don't expect much difficulty with the water circulation/filtering system either.