I get all the reasons to be pessimistic about Nurk (SOS, Smaller sample size), but the reasons to be optimistic that he is only scratching the surface of his ability IMO outweigh them. 18/11/4 is not out of the question for him next year for a number of reasons.
First, it's a fact that Nurk will play more minutes per game than he ever has before. Terry is known to only run his best players out there and run them ragged, so I expect Nurk to get a bit of the Dame and CJ treatment when it comes to minutes meaning 35+ on average. That alone would be a ~25% increase in minutes right off the bat giving him that much more opportunity to effect the game and put up those numbers.
Second, he has totally transformed his body this off season. This will allow him to be more effective over all of those minutes rather than just the first half. I expect this will allow him to finish faster and stronger as the roll man, allowing him to be more efficient in the P-n-R and around the rim. (I'm looking for +55% shooting around the rim he was around 53% with us last year)
Finally, he will know the enitre playbook and have sets designed specifically for him. Cj said last year he knew maybe half or two thirds of the playbook and was able to accomplish some pretty amazing feats. Familiarity and design should give him an extra boost next year. Around the league the reason for pessimisim about the Blazers comes from the unknown of how good Jusuf really can be. Can he become a top-5 center in the league next year? Time will tell, but I think the reasons to be optimistic are clearly there and he has the chance to put up some numbers that will suprise people.