Well,
Just because no one or, not many do not rank high for casino or online casino with a .nu domain does not mean it can not be done. Obviously a .com or .net domain is better but I have no reason to believe that it is impossible, nor that it requires a lot of extra work for a .nu domain. I doubt many have tried it to be honest. This is just my opinion, I could be completely out sailing here but I still feel the 10 year old domain has alot of promise 
Ill let you know how well I rank in a year or two.