According to Boeing,
http://www.boeing.com/commercial/air...ps/787sec2.pdf <Page 10>

8seat config is going to be 2-4-2, and each seat will have 18.5inch(47cm) width.

9seat config is going to be 3-3-3, and each seat will have 17.2inch(44cm) width.

Since 8seat configuration was what the boeing really advertised past few years, this is very exciting. Also boeing has specifically Economic Plus configuration with 7seats across, 2-3-2 with 19inch(48cm) width.