I would love to see 3rd Rail do something new and different like a Baldwin AS-16 or Baby Face. I know several roads used the former but sadly only three or four used the latter but it would still be exciting to see.
The F units and Geeps are some of my favorite locos as they are a great representation of first generation diesel power but I agree they are way overdone. All Nation, Overland, P & D Hobby, Kemtron, Hallmark, Atlas, Red Caboose, MTH, Sunset....
The golden goose can lay only so many eggs.