It's been a long time since I've taken the N'ex (I usually go straight to Skyliner or to Limousine Bus if departure time is close enough), but I've always found it almost empty, and I usually land during the morning (LH from FRA, LH from MUC, LX...). I have never think about the possibility of not being able to get a ticket... hope it doesn't happen (end of golden week) when I land there next Sunday...