Kudos to MTH for producing the scale 44 tonner. They will get LOTS of mileage out of their tooling as they can keep reissuing them in a myriad of road names.
Most of what's left to produce are locos that were made in small numbers or specific to just a few railroads. I would very much like to see a U18B or a GP18, but I don't expect to see O Gauge versions of these any time soon.