From everything I have been reading it appears the 787-9 could render the 787-8 redundant. Most carriers who had 787-8 order have switched a large part of them over and almost all new 787 orders are for the -9 & -10. It appears to be a trend as shown by the 767-200, the A330-200, the 777-200 etc. I guess the technology advances quickly enough during the development and build process that by the time an airline is ready to build the stretched version, its almost a 2.0 version in itself.

I have sent an email to some Boeing Wide-body sales people I met on a recent flight. Not sure they can give me the 'exact' information, but I'll follow up with any pertinent information they allow me to share.