There's stuff like NI's NKS [0], but it's highly vendor specific and very inflexible. I assume this will remain the case, given the relative variability of MIDI controllers - the position and amount of control elements, not to mention their implicit relationships (knobs that are directly above or below a fader for instance); and their near-universal non-responsiveness - there is no way to say, label a control for you to see physically.
Interesting issue to solve though, I'd bet my money on modular MIDI controllers becoming more prominent in the future.
Especially if you don’t have a predefined midi map/template.
Or is manually activating controls and defining your map still the best way?