Whether Jon is psychic or not, all the conversations you mentioned were brilliant bits of foreshadowing. I'm re-reading the series and am picking those out more and more - it's really amazing. And I bow to your argument - Jon is the one subverting the rules, so it shouldn't count.
I wonder if there are other examples of Jon cracking jokes... There's the time he told Tyrion "Maybe he thought you were a grumkin." - I wonder how we could interpret that
in light of this theory, lol.
Still - "You'll be sewing all through winter" is awefully ominous, IMO. I can just see the body count rising.