I really think that the overwhelming majority of people want to control their trains with a physical remote. The lack of the availability of a remote system really inhibits the ability to control Lionel's locomotives to their fullest extent.
The excuse that has been given is that some parts that the original Cab-2 used are no longer available. This seems mostly to be related to the B&W LCD screens. The other parts (sliders, knobs, and buttons) are mostly replaceable items. Buttons are buttons, and the the button grids on remotes are not going anywhere soon. The big red knob is likely a rotary encoder - though the one from the Cab-2 with detents is preferred over the version in the Cab-1 and Cab-1L. I think the sliders are probably just resistive, like linear potentiometers, but might be linear encoders too. Either way, there are a multitude of part options on the market.
IMHO, the screen is not essential to the everyday operation of trains - however an LED (or LCD) displaying some of the remotes operations would be a nice to have. I think ideally a two digit display showing the currently selected locomotive number and a separate 3-4 digit display to show the speed step, train brake value, and maybe other values as needed (smoke level, etc.) would be valuable user feedback devices.
I've mocked up a remote with the big rocks below. Obviously, I'm not an artist, and aesthetics take a back seat to functionality in all I do, but this should get the point across. The rest of the advanced, or "feature rich" controls could be reserved for an phone/tablet app or even a computer. In fact, moving that stuff (even things like train building) out of the remote and into a better UI would benefit everyone.