I agree on earlier posts that the limit is the airport designs.
I have always marvelled at the inefficiency of nose in parking. Once during apron works we had to park side on, and de-boarding/boarding all happened quicker with two sets of steps equidistant from the gate entrance. Bags were kept away from the passengers too.
A properly designed pier system with underground passages for service vehicles and provision to connect airbridges front AND rear would allow aircraft like the B777, A380 and B747 turn quicker. Smaller aircraft would benefit even more as they are not limited to the constraints of the larger long haul ships, slots and spacing to enable two flight daily cycles, etc.
Just a thought.