Very nice. I’ve been looking into the same thing, with a different video grabbing method though: A HDMI-to-CSI bridge (Auvidea B101/B102). Hopefully, this could somehow work with a Raspberry Pi Zero W, which is very compact and also supports USB-OTG. Unlike the Raspberry Pi 4, a single USB port can easily power it.
Unfortunately, the much more powerful B102 bridge isn’t available. :(