For what it's worth, I am far more interested in 4-axle diesels and smaller steam engines. They just look better going around 60" radius curves. Therefore, a correct GP40-2 in any phase would pique my interest.
That said, if a single SD40-2 reservation would make the difference (I doubt it), then I would place one to help get things going...but right now for me that money is better spent on other things. I have a VERY short 'want' list of 6-axle diesels (NKP and black Erie Alco PA, maybe an SD50).
I suspect my opinion is not representative of the masses, because it seems everyone and their brother owns a Big Boy or Challenger, haha.
Overall, it is a good time for O-scale. It would be nice if there were a company like A-Line/Rail Power for HO, cranking out undecorated diesel body shells in all variations so we can build our own.