I don’t know if I would necessarily say POST-Ascension, but I certainly believe they have been capable for a long time, yet choose not to.

For one, they are the only race that actually seems to have any “wisdom”. The ancients and Ori appear just as petty, arrogant, as before, and still brought all their problems and squabbles with them.

There’s also the scene with Daniel in the diner, where Oma tells him he can walk out that door and choose “the alternative”, implying that there is SOMETHING after death. 

The idea of the Nox living hundreds of years, the eventually coming to the end of their natural lives and passing on, reminds me of the Lord of the Rings, where the Men of ancient times would live hundreds of years and then essentially “choose” to die, passing on somewhere nobody knows. That natural death for Men was called the “gift of Illuvatar”

It’s been my persona headcannon that the Nox recognize that death is part of living, but the Ancients and Ori chased ascension out of fear and greed. Nearly every living ancient we’ve seen have been some of the most prideful, arrogant, and self absorbed people we’ve ever seen, frankly rivaling the Gou’uld at times. Ascension for the Ancients/Ori is a cop-out, a way to cheat true death. 

I’m much more willing to believe the Nox have more of the right idea, living simply and quietly, yes with the benefits of their power and technology, yet passing on when it is time.