There are a large number of devices able to send and receive MIDI CC messages. MIDI controllers like the DJ Tech Tools MIDI fighter twister and the Ableton Push 2 would in theory make great controllers for a flight sim. But there are also cheaper alternatives to let players get access to 0-255 step, tactile controls and as many programmable buttons as they want.
I would love to see this as well. I use a Behringer Xtouch Mini and it would be fantastic to be able to use it in Flight Simulator natively without having to hack something together with vJoy/midi2vjoy.