Baffles me this one. In almost any other game there are options to map any sort of USB controller. Throttles, button boxes, wheels, pedals, any sort of USB controller can be plugged in and assigned to any in-game control you like. It seems like this is well supported in the Unreal Engine. So why doesn't TSW allow it? It would make life so much easier instead of having to use the "Raildriver and Joystick interface" 3rd party software (which is, of course, a brilliant bit of software and better than nothing). It gets so confusing when, for example, the gear change in the 101 is mapped to the Loco Brake on the Raildriver, which you then in turn map to some other axis in the R&J Interface, and it gets so confusing trying to work out the correct pairings, and then getting the calibration right. I recently acquired Subway Sim 2, and this makes mapping my custom train controls an absolute breeze without needing any sort of middleware. Works flawlessly.
Honestly this should really be a fundamental access feature of any game. I'm still frustrated when I find the odd game nowadays that doesn't do it. I've been able to do it in many console games at least since my OG XBox. I'm glad it's not too common an oversight, or I'd be running out of onboard memory profiles on my XBox Elite controller for storing stuff like remapping the Rebel Galaxy Outlaw controls to match those of Elite Dangerous.
I'd imagine it's one of those afterthoughts that don't come up much. Personally, I'd would absolutely love this feature as I tend to configure my controller profiles in ways that doesn't break my brain.
Supposedly the API is due very soon, along with the accompanying editor update, that will allow direct controller support and more, according to Matt.