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No, the official stance is that we have "light" and "heavy" weapons, any reference to "medium" in the game text is a bug.
I don't think a new class of weapons will be created for this game. There have been rumors of an impact based heavy weapon called the minotaur that Muse is working on. I can't find the thread so it's likely only rumors. Still, I can't wait for a new gun on a charging spire.