If you ever intend to install the HDMI out board to use FPV goggles, the bit rate on the P3A will sorely disappoint. It's an unadvertised difference that bit a few P3A owners, after installing the HDMI board for goggle use. The P3P HDMI output is significantly better quality. Also, the still jpg images extracted from the 24 fps 4K video on the P3P are very usable at 4-7 MB each! You get 24 of them every second! Try that with the still camera capture! However, for dedicated still captures alone, there is no difference. The price difference is also less now than at original release, over a year ago. It's about $100-$200, instead of $279.
So using the HDMI output of a Nvidia Shield K1 from a P3A probably wouldn't be that great either for, say, a TV monitor?