Welcome to WWN.
I think some CPS patents are still valid and some are not any longer. Buzz Bee has released a cylindrical CPS blaster this year, so that seems good. I'd have to carefully check my patent listing
to see when the others expire(d).
This general idea has come up quite a few times. I'm on mobile right now but could dig up some links when I have a real internet connection. I should probably write a FAQ on this as well.
I think our best bet for wider acceptance is better homemade water guns made either by a hobbyist themself or sold by hobbyists to other hobbyists.
3D printing is not that good for water guns. First, it's expensive. Relatively small pieces will set you back around $50 each. (I actually can get things printed for free, but it's only for individual use and you better bet they'd cut me off if it looked like I was giving the parts away.) Second, it's not good to use under pressure because it's weak in the direction against how it was printed. The surface roughness also is bad, which increases turbulence and makes a bad stresm. Tim found that 3D printed didn't work better than cheaper nozzles
, even though the 3D printed nozzle was a special design found to be better for fire hoses. I think 3D printing has a role, but it would be for things you can't buy off the shelf or make otherwise. And don't expect it to be cheap.
Also, a while back I tried to sell water guns I built, but ultimately none were made it sold. I found that people were entirely unwilling to pay the costs. Due to economies of scale, small batches will be more expensive. $150-200 for a water gun would have been around what most people wanted would have cost as I recall. And that's making little to no profit. I think if we had a design that was made to be cheaper, we could get around this. I've been thinking about this a fair bit, but have put it on the backburner for the moment.
I also recall that iSoaker asked Buzz Bee what it would take to get a hobbyist water gun made in small batches, and it wasn't feasible. I'll dig up that link later.