A bunch of other SoC manufacturers have working system sleep implementation, either manufacturer supported or community supported. Never mind much faster boot o

A bunch of other SoC manufacturers have working system sleep implementation, either manufacturer supported or community supported. Never mind much faster boot options (like hundreds of ms to kernel). So you just need to pick one that also has whatever camera interface you need supported. Say any RK3399 based board can be made to boot to simple userspace in 1-2s and have working upstream camera MIPI-CSI drivers and ISP. System sleep is ~300mW so ~60mA@5V. Pick one with wifi onboard if you need that. And it's all opensource software, no binary crap that can't be optimized.