I would like to see "bottom hats" too for even more flexibility.
I am somewhat of an amateur at computer building, but I have combed over the A4 and M1 online quite a bit. This request for a bottom hat seems to have come before it was determined to allow for the PSU to be flipped. I would imagine in this orientation of a SFF case, one of the primary uses for the large top hat would be to put in AIO coolers. However, with the PSU flipped, its hot exhaust would either be pulled through the radiator, or fight the downward airflow. Assuming a non-blower gpu, you could have the same issue. An AIO in the top would either be sucking in hot air, or fighting natural circulation by blowing down.
If there could be an AIO solution incorporated in the bottom, then it would be pulling in cool air and not fighting natural circulation. From what I can tell, though, this may remove a good location for a SSD. As you have previously indicated, however, you favor the m.2 as the way of the future anyway.
It seems like it may be a major change at this point as I saw you are targeting early April for a kickstarter launch. It does seem, though, that it could be an invaluable modification. Also, on the top of natural circulation, even if an AIO isn't used, wouldn't you want hard drives below all the major heat-producing components? Lower would keep them cooler and not impede hot air escaping from the top.
EDIT: If the same hat design could be used on either the top or bottom, the possibilities with stacking them can really become more attractive to those on the fence.