Have you considered making updated hardware based on the Allwinner V5?
Development board: http://www.lindeni.org/lindenis-v5.html
The V5 SOC is under $10 and it supports dual 4K cameras with hardware binocular depth mapping. It also has a hardware HAAR feature classifier. The SDK is on github: https://github.com/lindenis-org
The CPU is same quadcore Cortex-A7 as the A33.
I have one of the dev boards and it has been working without issue. The only thing missing is the tool for using the HAAR classifier with OpenCV. Allwinner has promised this tool and say they will release it once it is working properly. Meanwhile they have provided about a dozen pre-built models.
The SOC also has the hardware to support 8-ch of PDM DMICs to build a microphone array. I have hand-built one and attached it to my dev board. I am able to do DOA calculations using ODAS. https://github.com/introlab/odas
I also have TVM runing on the board. https://tvm.ai/