Everything of these is possible.
Hell, the
Could you make garments like pants pockets and drop leg pouches etc and all the other garments into individual container style? (make us use those bullet holders and clip holders!!)
is already done. Just download the source code or compiled game from this thread and tweak .json files in HybridInventory mod folder.
Problem with rest of you suggestions is not in doing them, it is in maintaining them. As this is never going to be accepted to vanilla game, one has to periodically update his code with new changes in main project. More different versions are, more work it is.
By the way, even if you make every worn article into the container, make sure you keep some value on items for general inventory (items can be both simultaneously), many game features rely on the general inventory space area and having it at 0 does not work too well.