Well, where do you see a gap? The A321 can go to about 220 passengers, the 787-8 210-280. How do you want to design an aircraft with 230 seats and a OEW (do you mean DOM?) of 72 tons? Boeing is at the moment the leader in lightweight design.
I don't think that airlines want to open another separate type. The trick is fleet commonality, not variety...
Dani