Hey Bmann,
With all the great units, right down to the latest 0-6-0, it's time for a great 0-4-0. Please consider this.
Somebody over on Trainboard did a rework of the old B-mann B&O 0-4-0T. He changed the motor, did a bit of re-wiring, took the chassis from a SPECTRUM USRA standard tender. The purpose of the tender chassis is to build a live brakeman's hack to provide some additional contact and a place to put a decoder. It appears that he is cutting down an old MDC wood boxcar to make the shell for the brakeman's hack.
The thing creeps nicely on DC (he has not finished the brakeman's hack, so the decoder is not installed, yet)..
B-mann did sell a Pennsylvania 0-4-0 and tender some time back. It is long out of production. I have one, somewhere, but can not find it, now. It might be viable to resurrect it, depending on how the tender compares to say, the tender on the ALCo mogul. Further, it would be necessary to see if the motor that goes either into the mogul or the USRA 0-6-0 would fit the 0-4-0. I seem to recall that it was quite small.
If any manufacturer did try to issue a tank switcher, it might be a good idea to include a live freight car, caboose or baggage car to aid with contact or to hold a decoder, for those who use DCC.
If Minitrix can do a glaskasten, that does a fine job, of pulling a short train. If Fleischman can do small locos with motors in the tenders.... wait... Bachman and another small US based manufacturer did 4-4-0s, with motors in the tender.... this can be done. As to DCC.The glaskasten can fit DCC, and it's TEENY..... nice idea to have a boxcar, w DCC. Maybe sell one chassis, that fits the tops of their smallest box cars lines? That way, you wouldn't have to worry about road names and variety...people could swap the boxcar, of their choice. It would probably sell to 0-6-0 owners, with slopeback tenders, as well. Just a thought.
A live caboose or boxcar isn't really necessary. A "keep alive" circuit should suffice to bridge dead frogs and bits of dirty track. The only limitations on an 0-4-0 is getting enough weight in it so that it pulls a decent sized train. The Pennsylvania Railroad's A5s (biggest 0-4-0s built in US) were good for about 12 to 20 cars - depending on how many horsepower per ton you want to base that on. So a more generic model should pull at least 5 cars on a slight grade, and 8 on level track. In practice, for tight industrial track, it probably wouldn't move more than 3 or 4 cars at once, but you just know that someone is going to want to pull the Breakneck Ltd. at Warp 9.5 with one, so that should also be factored into the design. ;)
Am I really alone wanting this? It won't have to pull a while 15 car SP Daylight, while pushing a UP Excursion train, up a 4% grade. Maybe just a few cars, smoothly.
How about anything small, that's never been done well?0-6-0 side or saddle tank?