Most likely, they well be together in S4. They are getting build up in S3, it's really rare to see Nate hang out with girls, So since there having tons of scenes in the second half of of S3. I won't be surprised if they become a couple in S4.
I'm pretty sure they will get togheter eventually, but I don't think it's gonna happen in S3, since is quite coming to and end, and if jenny makes Nate and Serena split up... it's going to take a little bit for Nate to forgive her u.u
Anyway I'm hoping for next season!! They will be an amazing couple, i loved them since season 1!
Since Taylor mosmen wil only be in the second half on the gossip girl season 4 im saying season 5 most likely and leave nate to devolp feelings for her in seris 5