Hi Again,
For the record, I don't think the inventory system is "broken" (as such), but I do find it cumbersome at times. 
OK, I do understand that human organisation can and is currently used to arrange inventory items, but that "filtering" items could be potentially useful.
And all that should (in what I am trying to explain) remain exactly that, BUT with an in-built "party search" system (if you like), that categorises the search. i.e. What I am probably poorly trying to explain (due to my subtle change a few posts back from the original, which may have been missed), is that the system effectively remains unchanged with respect to encumbrance and inventory slots, but has an additional "party search system" where the player can pull items from the party inventory and place it into the PC inventory (currently open) instead ... without having to switch through various other PC inventory screens trying to find it.
Picture the inventory screen with "extra tabs" (situated somewhere else accessible), that opens item lists (possibly to the side) according to categories represented by each tab where the player can then drag said item from the list (if need be) onto the current PC inventory. This shared "tab list" would effectively be a "container" (like a recipe book) for sorted items that the party carries, which is NOT accessible by the AI (so no problems with shared there), but is accessible via code when it comes to things like crafting checks. (NOTE: I know the modern recipes do work in a similar manner with respect to checking items in the party, but this would be a convenient way of checking other styles of crafting too.)
As another example (showing the differences): I like the idea of any PC being able to pick up an item (like a gem or crafting component) and it being placed inside the party "bag" for such items. Now, it can be considered that each PC might carry their own bag for such, or (for player ease), a single party bag is allocated in such a system. Bear in mind, that the latter (party bag) is what I originally considered, whereas, the former (each has their own bag) is what I am now proposing, but that this tab system would list all the gems (or whatever tab item was selected) from all bags of all PCs. Whether each system has benefits both from playing or performance, is up for debate.
I'm still juggling the idea at the moment, so don't assume the thing is set in stone, As I say, that's the point of this discussion.
Cheers,
Lance.