UAL's oldest 777's, the A's, have 364 seats. The new 300ER's are 366. The A's are a candidate to be replaced in the net 5 years or so. 1994 is the oldest.

So, the 787-10, not really a replacement for the A's. Unless you put in cattle car seating like the A's. 10 across in back. Sardine anyone?