in the studio, for gear that keeps a lot of info buried in contextual menus (e.g. DSI evolver) I like having a computer based editor on hand as a heads-up-display and for setting certain Parameters. I think such a program would add to the zaquencer experience at least for me.
It could be combined with a librarian to help manage storage/import/export of tracks/patterns/banks. I imagine that being able to pull and recombine from an archive of tracks and patterns, complete with instant at a glance visual feedback, would make the zaq a more robust sequencing platform.
I know that the librarian features can be somewhat accomplished via Midi-ox and Windows with a little legwork, but I think streamlining them into an editor that simultaneously provides a full visual readout of the pattern content takes it to a new level