Given enough time, resources and finances anything is possible, however let's say someone started developing a gimbal for the GP6 to use with the solo. in a years time they have it ready and done with. Full compatibility, full camera control, however cost would be... $600 per gimbal. Question is, who the heck would buy it? In a years time, who knows what drones will be available, how much they will cost, what the camera's will be like.. etc. Plus the market for the 3DR solo is diminishing due to limited supplies (no one's making them anymore). Plus in a years time, GP will come out with new camera's.... so you're always playing catchup.
Most people probably bought the 3DR because it was just so darn cheap (ahhh, the $300 days when it came with a gimbal..). So they may be reluctant to pay $600 for a gimbal for what they see as a $300 drone) (or less depending on where they bought it).
Even if a plug and play solution was designed and working, to lower gimbal production costs, one would have to mass produce them which would require financing. That's a lot of commitment for a drone platform that's no longer in production and for a diminishing market (hey, stop crashing your drones people!).
We all would like a new gimbal that supported other camera's, gives full camera control and works with smart shots, however without a sustaining market for them, I think the most we may see is some instructions on how to build DIY solutions that only offer partial functionality..
I'd love to be wrong on this of course, but I'm just not sure it's likely..