I mentioned this on another board, but consider that there have been very new few 4 axle locomotive frames produced in North America over the past 2 decades - right now there are a lot of GP38s available for short lines and switching roads, but soon enough they’ll wear out - and a small switching shortline with tight curves is gonna use a third-hand SD70MAC?
Even the Green Goats and gensets are NOT a solution to this problem, as they re-use GP7 and GP9 frames - no new 4 axle frames are really being made (and they could be, and sold to smaller locomotive manufacturers and rebuilders).
I DON’T trust the North American locomotive industry to address this problem until it’s much too late, and then they try to play catch-up with second rate products…