I really like the direction you're heading in and will be interested to see the results. I have been working on some simple way to rotate the stone or lid during cooking but it is easier said than done at these heat levels and have also contemplated a design similar to the one you are proposing. I currently have a rotational set up for the stone that works, but is not ideal - I will post pics if people are interested.
The potential issue I see with your design is that you will really be pinpointing the airflow to very specific spots and this is likely going to direct a really narrow and intense stream of hot air to a small area and result in strong hotspots - if this happens, you will need to be constantly rotating the lid both during heat-up and cooking in order to distribute the heat - also, heat-up times to the entire stone could take a while.
Also, with such a narrow airflow pathway, I'm imagining that you will not be able to turn up the heat very high before it starts sending the heat straight back down toward the base because it will bottleneck at the small opening along the lid, so the heat will need to escape along the path of least resistance (back where it came from) and this will result in a lower overall temp and long heat-up times
I'm wondering if making this opening extend to a larger portion of the circumference (maybe about 1/3 or more?) opposite the side vent may allow for a larger volume of air to escape to a larger surface area? What do others think?