Femto, ANAL, of course so I can not really help on the legal issues, I only can reply as an engineer who happened to run an open hardware company for more than 10 years. From the very beginning of our business we never licensed any products by anything other GNU GPL and GNU FDL, just recently added CERN OHL as it became available.
Legal stuff is important, but I do not see a big problem in "gentleman's agreement" in the areas that do not yet solid legal basis yet. Our use of GNU FDL for the hardware documentation is also a kind of such agreement, and it did work for us all these years. Yes we do know of some violations of such un-enforced agreements by our clients, but great products and the user freedom that adds to the value, can do much for your protection.