Everything I've seen in Aviation Week and elsewhere says twin-aisle. The fuselage weight penalty for an extra aisle is not that much, and considering that the fuselage is widely reported to be elliptical I'd say the penalty is almost nil (because the fuselage itself will generate lift). Also, Boeing is putting folding wingtips on the 777x, I'm betting the same for the 797.

My bet is a widebody with a fuselage no longer than a 900ER and folded wingspan no greater than a 900ER. So, we get a twin aisle aircraft that fits inside a standard narrowbody gate with efficiency that at least matches a -10 Max and probably exceeds it significantly. Would be wonderful on our most congested routes and into our most congested hubs. Winner.

We're gonna need a bigger boat... I mean, passenger waiting areas.