After few months of release of a new MacBook Pro with Touchbar (I'm writing this from 13" model MacBook with Touchbar and I really like it) we got dedicated MIDI controller and it is Free.
MIDI Touchbar allows you to customize surface with faders and keys (Keys are marked 1,2,3...). It seats in the right part of your touch bar and works excellent - when you need it you just touch little midi icon and it expands to take over the touchbar.
So far only Logic, GarageBand and KORG Gadget brought support of touchbar (KORG Gadget has MIDI keyboard while Logic/GB has multiple layouts for arrangement, instruments/individual channels control and so on).
With MIDI Touchbar you can get advantage of MacBook pro's touchbar if you are using Ableton Live, Bitwig, Reason or any other DAW (it even would work with Maschine and Reaktor standalone).
I hope to see more tweakability (custom CC's) and dedicated midi keyboard (like in Korg Gadget) in future versions of MIDI Touchbar. But it is already great solution.