It would be an unbelievable move if Utah could land Nash. Obviously you'd worry because of his age but the guy is such a freak of nature, just put him on a similar rotation Jerry used for Stockton after age 35 (32 min per game, come out at the 4min-mark of 1st&3rd and re-enter after under-9 TO of 2nd&4th regardless of score). It would be imperative the Jazz have a competent backup but Nash not only improves the on-court chemistry, he'd improve the lockerroom and huddle as well.
It wouldn't be a perfect fit - it's easy to compare Nash to Stock because of their age/effectiveness but his game is completely different, Stock was as efficient as a robot, same sets, same plays, if the defense did "a" Stock would do "b." Nash improvises more, does alot more probing, dribbling aimlessly until he creates a passing lane for a teammate, ect ... so Ty would have to loosen the reigns a little more (i.e. less iso on the low block and lift our bigs to the high-post to create the spacing that Nash needs to thrive).
He'd give Utah a 2-3 year window to develop younger talent to eventually become the longterm answer at PG, he'd keep Utah super competitive and he would get all of our bigs some great looks.
Ultimately though, I don't think Nash would choose the Jazz on his own because if he leaves Phoenix his goal will be to win a championship - and Utah isn't at the level yet. Becoming a legitimate championship contender is a multi-step process over multiple years, and the Jazz have only reached Step 1.