Adam Malkovich from Metroid the Other M should be an assist trophy for sure. I would say he would make a good character, but I don't think 1 game as a supporting character at this point cuts it. I don't even know if much wider known characters such as Waluigi should make the cut, so Adam is out of the question at this time for me. Adam would be a great addition to the assist trophy collection, though. He could go out and shoot at you similar to Saki from Brawl.
I think if Adam continues to play an important role in the Metroid series, he would be a great addition to Smash Bros., especially with a major series so low on character options.