Boeing's small widebody planes / New Midsize Airplane (NMA)

Right - but you still have a problem of two aisles. It is a LOT of empty weight being carried around.
The benefit is faster people movement - the question is of those two can balance ?

Neither 3-4 nor 4-4 could be certified, as such configurations don't meet the following safety requirement, which is unlikely to be relaxed : no passenger may be seated more than two seats away from an aisle.

That's the reason why narrowbodies are 3-2 or 3-3, and why any seven-abreast seating requires two aisles.

I doubt widening the lower cargo deck without taking advantage to go for eight-abreast seating would be clever. On the opposite, going seven-abreast with a reduced cargo hold ('flat' oval fuselage) is among rumoured options.

Flightglobal provides some information about Boeing's new widebody project, now dubbed NMA ('new midsize airplane').
www.flightglobal.com/news/articles/paris-boeing-partially-unveils-new-midsize-airplan-438512/

The airplane would be mostly CFRP and would have a very high bypass ratio. Most interestingly, it would feature a 'hybrid cross-section', i. e. a widebody passenger cabin and a narrowbody cargo compartment

Interesting, thanks s543!

(I've modified the title if it's okay)..