The general contention I recall from prior years was that Nate was a great coach for a team that is building, but is probably not the guy that can take a team to a title. Or in otherwords, he can get a team to the playoffs, but doesn't seem to have the chops to do much when he's there. I don't think that perception has changed much.
As it stands, this is not a team that anyone believes would be a title contender even under Greg Popovich or Phil Jackson, so I think Nate is probably good enough for what we have. Extend for 5 years? No. Extend for 2-3, sure.