I think pokey willl make an appereance. Here is my reasons. First off, in earth bound, I always did think he looked and acted like a pig, so he should have some role with the pig army. All EB games are connected in many ways. Now that I think about it, the game never really says his plan.
Music again is a connection.
Comic like text and charecters. So this is why I think pokey should and will be in EB64. At the end of the game it states that pokey is gone.and not to mention the letter. SO here is my theory. In EBZ Giygas leaves vowing revenge.