Well, I'll never see a new NB in my career I don't think. I'd actually be pretty happy with the 737 if they could just add these:
1. temp controls that worked and you set a tube temp (78F) and it automatically held it. And move the main controls back to the cabin so those who feel it can tweak it!
2. Place to store my bag! Just increase the size of that cockpit bag storage a wee bit, 1" horiz and 2" vertically would do... EASILY DONE if you'd just move that stupid fire extinguisher up on the bulkhead behind Capt seat.
3. Fix the stupid intercom/FLT thing so you can wear a headset and talk to the other guy without uncovering your ear and going deaf, or having to reach down and push the actual MIC switch in wrong direction to chat every time. Voice activated like every single motorcycle helmet setup and light GA plane.
4. Put the FMS button brightness control for MY FMS on MY FMS... not on a single control that tweaks allllll the other switches. With 900 buttons being different than 800/700 FMS buttons, I actually have to be able to read the things at night now to hit the right ones... and the left seat guy's idea of what's good never seems to work.
5. Redo the autothrottle control algorithm to a "never exceed" control algorithm for the redline zipper... the closer you get to the zipper, the more agressive it is at staying on bug or below, NOT drifting higher to within a knot of MX overspeed.
6. Fix the dang toilet seats to stay up when lifted.
7. soft rubber covers for those switches on the overhead I always bang my head on when standing up.

That's it. Some small tweaks would make the thing livable.