First- I don't want to run my trains with a cell phone, or any other touch screen device.
The RailPro device you "like" is pretty much a smartphone device with a rotary knob. Everything you do on that thing is touch screen except turning that knob. If a turning knob is your requirement, why can't rolling a joystick in a circular motion CW or CCW accomplish the same feeling.
None of the controllers in the image above except possibly the last one could be used one-handed.
Some other controllers that are also not one handed - Cab1, Cab2, MTH DCS Remote, Railpro, CVP Airwire, NCE ProCab. While some functions can be operated with only one hand on these devices, their design still requires two hands to properly use the remotes. I don't know of anyone with long enough thumbs to reach the big red wheel on a CAB remote without using their other hand. This isn't an argument to say that app-based remotes are one-handed, but rather that every remote available to us (past & present) requires two hands for complete operation (except maybe the Lionchief remotes).
I'm still hoping for a CAB-3 to go with my BASE-3. Perhaps Lionel could make a deal with one of these companies?
I believe that the path forward for a CAB3 hardware remote will be utilizing the current CAB3 app with an add-on peripheral. I think that it would be very possible for Lionel to build (or contract with a 3rd party) a device that works exclusively with the CAB3 app.
