I think the workname "-900" is a project name for an all new family.
New fuselage, new wing, engines, everything.
Being a new family it will probably build up out of various capasities.
80-100-120 seats? A different segment also, directly entering the Emb 190 / CSeries segments. Maybe it will be 5 abreast.
GE and RR are working on new engines in the 5000-8000 shp category. I think most people feel fuel will pass $100 as soon as the current storm lower and OPEC re-unites.
This will lead to fuel economy and operating costs climbing higher on the priority list then e.g. speed, range and comfort.
For your entertainment; not so long ago I did a simple sketch on a fast 100 seat Turboprop with GE38 engines, Thompson seats and scimitar blades, a kind of SuperSaab
