I think this is an interesting topic however, i think we should define what is the goal of the project. Should it be a low cost item, what are the parameters such as speed, number of channels, screen size, screen resolution, touch screen, number of settings and many many more.
With regards to the legality side, if it was made as a NFP or even sponsored by a tech company then it would be considered legal and above board.
Consider this if we would get sponsorship from Rigol and/or Tektronics or some other brand that could assist in some way then they could guide us away from the patented issues. They could provide support in finding or suggesting parts, testing solutions, issues to avoid that they have encountered, we could all learn from the big guys.