I think an SD card slot to save your presets, etc would be nice. Then you can work in Native, save your work, and load it into the helix unit. For live it would be great if one of your Line 6 units craps out (or someone throws/spills a drink on it), you can easily replace it with a back up unit/spare and restore everything in a few minutes. I realize you can do this with a laptop but who wants to carry a laptop to a gig and realistically a back up unit never really gets updated with your new settings on a regular basis (who has time for double work).
