What days of the week? I had no problem clearing a late April DEN-NRT-DEN on a Wednesday outbound and Monday return, though it did take several months for the seats to open up (booked the prior May, cleared in January IIRC), and after the 787 was grounded, had no problems finding R space on DEN-IAH-NRT-SFO-DEN (though I would have asked them to force it open should it have been an issue).

Obviously, on peak days, chances go down. The 787 doesn't have a huge amount of C seats compared to, say, the 747 ex-SFO.