Regarding Key Items Tab:

People always feel like that tab is extra inventory. It isn't. It's a visual representation of a checklist. As far as the game is concerned, those aren't "items". The game just has a checkbox either checked or unchecked if you have access to "thing X". I'm not even sure it has a limit. That is, if you somehow managed to fill all three tabs and get another item, I'm not sure what would happen - if the checklist has a cap or what - since every character has the ENTIRE checklist referenced on the backend. You DO have a limit of how many quests you can have at once, so it might have a limit like that, but it's not based on "slots" or "inventory" in the normal sense of the term.

I think Yoshi P has even talked before about that and that being why those can't be converted to extra bag space, since they technically don't exist. Think of them more like a spreadsheet listing things your character is flagged to do (interact with quests) rather than items.

In that sense, it's the same as your currency tab, where it just has you flagged as being able to do X thing Y times.

I think given all that, it'd make sense to just make the totems currencies at this point. It's not like we don't add 3 new Tribal currencies each expansion. And they could make them like Tomes where, when the expansion was done, they all convert to "Reborn/Heaven/Storm/Shadow/End Totem" that you can use to buy any of the things from that expansion (with the caveat you have to clear the Ex before you unlock the things you'd buy with that Ex's totems). It would probably actually SAVE data/server resources to do that than keep the system we have now for perpetuity.

(While they're at it, they could do something similar with Bozja stuff...because good god there's a lot of stuff, even ignoring the quest-only items and focusing on the regular inventory stuff like the Memories...)