It is simple and it works well. I have never found it lacking, once I shoehorn myself into the seat that is! Serious question.
The 737 is not 'simple' by any stretch of the imagination, from a system design and ergonomic position the thing is a nightmare. (the fact you can inadvertently pull the gear up on the ground says it all really)
Given that it was built post 747-400 it would be akin to buying a nice new commodore and sticking a 1980's VL interior and dash in it.
Yeah it is reliable, has high utility, very flexible, awesome range and performance but the cockpit is a horse's arse.
The 777 or the 744 cockpits are what the 737NG SHOULD and COULD have been.
How many times do you need to creak you neck over and back to check stuff? What affect does that have on ones body over 10000 hours+?
Not to mention the windows and noise.....
In the 1970's they weren't building aircraft with designs from the 1940's now were they........................