Big Al and Nash wouldn't work well together offensively. They both need the ball in certain situations (Nash in pick and rolls, Al in low post) that are the opposite of what the other one does well. Given their combined defensive flaws (and how much it would impair rebuilding), I don't think this trade is worthwhile making.
Even if it was worthwhile, I don't think it is realistic. A 29 year old struggling Devin Harris is not enough to tempt Phoenix to make this deal.