Some things lead me to believe that Diego will be used on the right of a 4-4-2 as a "semi-winger." He did play there at times against Red Bulls, and although DN wasn't in charge yet, they may have been experimenting with him there. He obviously likes that system, and I don't see us getting the minimum 2 winger signings we would need, so Diego might have to suffice.
Also, we don't have any backups for him in the trequartista position (apparently Gio doesn't fit there) and that position would also require a signing. We have 4 forwards, (3 if Trez leaves + not unlikely Pizzani) so I would guess we would use 2 forwards, meaning there can be no wingers AND Diego.
Of course, if we go with Suns' favourite formation, then everything said above is null.