Yeah, I don't see it. For example, comparing MP Megatron to his G1 incarnation is like comparing apples to oranges in that the only similarity is the name they share. They are completely different moulds, vastly different scales, and don't even transform the same way. Also, as far as I am aware, Hasbro owns the trademark 'Shockwave' so there are no issues there (it was used in Animated and more recently in DOTM).
A MP Shockwave similar to the design of the
Palisades Shockwave statue - which was licensed, would be doable. Besides, whoever now owns the copyright for Astro Magnum (if anyone actually does) would not own the copyright for the 'generic space gun' design.