I think the karma will sell quite well to the audience it was made for, which is the action sports crowd. I don't think it will outperform solo as solo was built to be more of a cinematographic drone. Don't forget solo also only had 2 point cable cam when it came out and didn't have all of the smart shots it does now. They expanded it's capabilities a lot during the 1.5 years. They could always improve karma over time as well via software updates, and gopro is pretty good about updates for their cameras so I think it's reasonable to assume the will do so with this new quad, which greatly expands their business model from that of just action-cam.
But the key to understanding what it's capable is still unknown and that is what kind of processing power it has/companion computer. A PX4 by itself doesn't mean that much. It's what's going to drive and send commands to that PX4 that matters more in terms of what it's capable of in terms of processing. It's not hard to fly straight from x1,y1,z1 to x2,y2,z2 (2 single points in 3D space) and doesn't really take any calculations to do so. It's a lot harder to calculate a curve going between those 2 points as you're potentially creating hundreds or thousands of intermediate x,y,z coordinates depending on how far apart those 2 points are for it to fly through each to make the curve in real time, or close to it. Then throw in speed and time control calculations. Then throw in automatic gimbal control and other precision, smoothed calculations based on time. There is a heck of a lot of math going on to do things gracefully.