I own a P4Pro plus and recently became interested in using it for 3d mapping.  Particularly pix4d or DroneDeploy.  Is that even possible?  If not is there any other software that will do something similar that will work on the plus?

Not possible yet, it’s a pity maybe someday soon.

Pix4d is capable of being integrated with DJI products but will cost you thousands to use.
Drone Deploy is also an out and out professional software. They offer a very basic downgraded version for free but are aimed at software rental costing 100s of $ per month. I guess it is DJI compatible, they use DJI drones in their advertising. There are alternatives, check out the web.

I think part of the problem is "+" on the p4 pro +.  Not sure they allow any 'apps' into the system.  Maybe there is a workaround or a different mapping software?

Not possible.
You can't load any 3rd party apps on the Plus and since it's been that way for almost a year now, it looks like DJI have no intention of changing that.
You can still use your Phantom to run 3rd party apps but you would have to buy a regular P4 pro controller.

So i can buy a p4 pro control unit, then somehow disconnect the 'plus' and hook into the regular.  Is that easy?

fans57af08bd Posted at 2017-11-4 16:46
So i can buy a p4 pro control unit, then somehow disconnect the 'plus' and hook into the regular.  Is that easy?

Not quite, you buy a P4P 'normal' control unit, not the plus model, use your own phone or tablet as the viewing device, then link it to the aircraft.

fans57af08bd Posted at 2017-11-4 16:46
So i can buy a p4 pro control unit, then somehow disconnect the 'plus' and hook into the regular.  Is that easy?

The P4 pro+ and P4 pro use the same aircraft. .. The controller is the only difference
To connect a different controller is easy and only takes a minute.
Go to the manual and do a word search for LINK and it will show you how.