Just seen this on YT - not sure I would have the need to have a second controller as he Mavic is quite different set up to the inspire. He mentions a use for teaching, but they aren’t that difficult to teach if you are standing next to the person flying.
Seems a strange choice for a firmware update especially as it seems you can’t buy a second controller from DJI (yet!) but for those few out there with a Pro and Zoom, well something new to try 
Saw a vid on you tube other day about the up date.
someone could use the other remote for photo’s/video and the other do the flying
Albeit with the MP, I never found flying diagonally and panning/tilting, and having to change the diagonal flying as you panned … all at the same time … ended up with very smooth results … and one of the main reasons I started using Litchi in zip-wire mode, or without pan/tilt in the mission to leave that as a manual operation.
And with the M2Z you have zoom to add into the equation.
So, I can see a need for pro video work needing that smoothness of tracking …. or where one needs to have more precise control of the drone than a spotter can provide.
Thats what I believe the purpose to be. Interesting!
Aparently, it also allows for the the Updating of Go4 and Pilot independently of the firmware!? again, kind of interesting.
(but I’ll not mention Litchi compatibility! 
)
That’s for the smart controller - this thread was for the default controller.
(That was the mistake I made when I move your post over to here - briefly).
Litchi works with a phone and default controller with M2P.
Yes it does!, I can vouch for that each time I link and unlink the standard controller. Litchi works just fine with the standard controller. 
Imagine dual standard controllers … both with Litchi … #FIGHT! 
I think this’ll be more for the Mavic Enterprise line for business users. Where health n safety risk assessments say one to fly and one to film etc perhaps? Just a hunch.
My monies on the lighter tighter standard controller!! !The smart controller trying to shift its heft about aint gonna happen! lol