I think the most likely thing is for Phoenix to allow Shaq to expire next season; I don't think they'll want to take on other salary commitments. If they do do a trade, I think it will be for other expiring contracts, plus either a young player or a draft pick.
As for Nash... it's hard to think that they wouldn't pick up his option. If they don't, it's hard to say where he'd end up. He's always talked about wanting to play in Toronto, but I think Portland would be a good fit for him.