Maul hiring Fett has a certain 'it rhymes'ness about it (what with Vader doing it in ESB).
Maul could be a carry over character like Dooku is in ROTS but he lives on either as a cyborg or a clone army.
If Qui-Gon continued over into the beginning of AOTC his return in the form of a ghostly voice wouldn't feel so tacked on either.