THIS.And IMO, the real hurdle to open source paintball gear is manufacturing, not legal issues.
Lets put it this way, if somebody wants to do a stacked tube spool, just 1, we (J4) would let them if they promise not to sell it. This is a 'for you' gun. Yep, no problem. There would be a small fee (VERY SMALL) just to cover the paperwork and such. And maybe buy us a beer at an event. We would even give you some CAD.
But it will cost a LOT to build it. Even if you have all the permissions. Less so if you have a machine shop.
Open sourcing could be just building an inline gun and using existing internals. Yet even that is rare. How many Evil-M's are built? Even if it is an epic gun?
The CAD and design could be done, permissions granted, but in the end the cost to build the gun (and I have built....20+?) at a 1 off or short run is expensive. For a gun that might not work if you changed the design too much? And will most likely will have to re-machine?
Since most of us don't own a machine shop, expect to pay $1500 for an airsmith or small shop to build you a gun with basic externals. Expect to pay $3000+ for a CNC shop, if you know the guy. For prototype runs from a few shops (Spurlock/Valveflow) budget $10K.
Even the new 3D printers, that do metal and did a working 1911? $12k for the gun. Just one.
Making it is the expensive part.