I wasn't sure where to post this idea, but here goes...
I just saw this today. An open source app (midi2lr) that lets you control LR via a midi controller. The obvious benefits are that you can have a hardware or virtual (think IPad based) device with dedicated analog controls (sliders, buttons, toggles, etc.) custom tailored to interact with AP.
Take a look here to see what I mean.
http://petapixel.com/2015/08/12/midi2lr-an-open-source-app-that-lets-you-use-any-midi-controller-in-lightroom/ (video at bottom, 1'41")
What a great interface for interacting with a photo editor!
There seems to be 3 components needed: 1. AP API (possibly via the Extension specification?) 2. MIDI2LR (fork open source project to create MIDI2AP) 3. Midi controller. These range in price from $ - $$$.
Is their a high-level API for AP to allow for this type of input? Maybe via an Extension? Not sure as I haven't been able to find any documentation around this specification.
Here is another example showing LR being controlled with an inexpensive midi controller.
Thanks for your time.