The wheels are not the problem here. Also, if no one wanted these conversion sets, it would be easy to find MTH wheelsets... they are impossible to find. Even when they were making them, a run would come in and be gone instantly. Excluding Lionel and early MTH, just about all the other diesel locomotives are pretty simple to convert because the wheels drop out.
The MTH 3-2 truck "simplifies" the matter because its pre-wired for either way with the flip of a switch, but there is a mess of wires on top of the truck and its a pain in the neck to sort it out if you have any kind of conductivity problem.
The axles drop out of modern Atlas diesels individually. Swap the roller and its insulator for a wiper and its insulator, change the wheels and you're on your way. (I think you can even buy NWSL replacements if Atlas doesnt have em).
Weaver horizontal drives are a wheel swap and a rewire.
Red Caboose (and Atlas/Roco), same thing. The wipers are in there either way. You can just replace the wheels and toss the rollers.
The big problem you have is the handrails.
On something like an F unit, its irrelevant, which is why you see Atlas providing a replacement pilot with the 3 rail models.
On any narrow body unit, all of the handrails need to be replaced, as the ones for a swinging pilot are short. Stocking the handrails in every color is not feasible for the possibility that someone *May* want them, nor is supplying 2 sets with every locomotive.
You could overcome this by doing what lionel has started to do, fixed pilots, a big hole in the pilot and an O54 (27"R) minimum curve. The compromise being that to 2 rail it, you have to shove a filler in the pilot (but I guess with some filler and black paint, thats no problem). Breaking the 3 rail size of their very small curve radii will be the hurdle there. The pitchforks will be out if everything suddenly needs an O54 or O72 curve when it previously didn't.
The other problem you have is the way the couplers mount. A lot of times its a one way conversion to 2 rail, as you need to remove the truck mounting point for a lobster claw in order to have the space for a kadee box to sit there and not be in the way of the truck swinging back and forth. If you 2 rail it, its 2 rail (or at least 3RS for good), and people who tend to grow tired of engines and move them to make room may not like that.
I dont see the control system thing being a problem. DCC is standardized as has been pointed out, and by and large, the sounds are better and the hardware is cheaper.
Honestly, its a tinkerer's/craftsman's scale. Doesnt bother me as thats what I like to do, but it just seems to be thats the way it is. Sure, you can buy everything off the shelf, lay sectional track, pull an engine from a box and go, but that doesnt seem to be the 2 rail way.
This is just my opinion, but O scale is like big HO. 3 rail is what it is. There is more in common between 2 rail O and HO than with 3 rail. Someone mentioned that pulling HO and N scale people was a good idea, and honestly, it is. All you need to do is explain that you can actually see what you're working on without tweezers and a magnifier, and bigger speakers make better noises.
