I'll start. I would make remote start an option so I don't have to go out in the snow to start the tractor and get it warmed up until I am ready to work.Maybe sliding windows on side of cab.
I certainly think remote start would be doable if you wanted, would just have to make sure you left the tractor in a "startable" condition... neutral, brake applied, etc...
I also think window defrosters would be good, but they may already be available... not sure.
I am an engineer, money is no object here, spending someone else's?! Why not add a heated-seat option, heated steering wheel, maybe a chilled seat & steering wheel for summer. 500hp engine w/1000 lbs of torque, that burns pints/hr, instead of gallons/hr, automatic traction control, anti-lock/skid brakes, 10 remote-hyd hookups as standard, I could go on & on & on.
Flat rubber gasket mounted glass in the cabs. The he!! with a $700 "rounded" glass frameless door!
For that matter, prety much all glass is round in todays cabs, sending you to the dealer with your check book instead of a glass shop with a few $20's. Just keep the weather out and don't worry about looking like a sports car.
Total redesign so you had skid steer like visibility when doing FEL work, and good rear visibility for rear implements. Maybe sideways seating for visibility both ways, like some asphalt rollers. Or rotating center seating with a tractor that was bidirectional.
I have thought about remote start and I have a kit for a car laying around:scratchchin:
Backup lights would be nice so the rear work lights don't have to be on all the time.
Heated mirrors would be nice too.