I think many of your complaints (which are all valid!) are better levelled at the normal Macbook and Pro line. It has bothered me for years that my first Macbook from 2006 had user-upgradeable RAM and storage as well as a replaceable battery. There is no reason in 2022 that the hardware engineers at Apple could not design such a machine again. These things are not IP rated so there is no need to close everything off from the user.

However, the Air line is sold on the idea of them being the thinnest, lightest laptops around and having open access would invalidate this somewhat.

As for Thunderbolt 3? I wouldn't hold your breath. The iPhone 13 Pro is still lumbered with lightning and its USB 2.0 transfer speeds. Given the device is advertised as being able to shoot 4K video it takes an age to get it onto a desktop.