I think Marvel Netflix is going to continue to grind out new seasons and stuff, but it's never going to hit the same highs. It'll be like most Netflix shows - like, there's a new season of Orange is the New Black or House of Cards, and everyone's like "oh, look, a new season," and then they watch it, and then they move on. Defenders is sort of like that, but for four shows at once.
Of course it really depends on Punisher and JJS2. Punisher is their most mainstream property since Daredevil (probably even bigger, honestly), and JJ got a lot of attention outside of the usual superhero media circles, so I think either of them could draw a lot of eyes.
But DDS3 and Cage S2 and Iron Fist S2 it's like... nah. Not fresh. They're retaining their viewers at this point, not attracting new ones.