@3. Could you elaborate on why the interface is painful? Just a brief rundown. I was wondering since other hotkey mods have done this already. Has some of the new funstions of your hotkey mod made it harder to make new hotkeys?
@7. Did the Gear-Set hotkeys previously show as the icon the last item bound as part of the set? I personally think this could work alright for them as you could assign last an item that represents the set to you, e.g. a cuirass of that armour type. It wouldn't work well for a cycler of course as you would have many items/spells/gear-sets. But yes custom items sound cool.

#3: it hadn't occurred to me that it was already possible until I started writing out #3. I've glanced at the code, and it is sorta possible atm, but I think it will only work correctly if you hold the key down for at least 3 frames. And the ini configuration to make it work is a little strange. Also, making 5 or 10 of them would take more CPU than is really necessary, not that people need many of them.
#7: Well, they sort of did, but that wasn't intentional, and it didn't persist across saves. It could be done intentionally though, wouldn't be difficult, and would then persist across saves.
In order of personal preference: 5,7,4. Showing the potion selected would just finish the potion hotkey and polish it up. 7 is also polishment, not nessecary but maybe I am a svcker for ui polishing.

4 is creating more flexibility, which is always good.
5 isn't terribly difficult though it's not exactly easy, but the big problem with it is that atm Pluggy causes crashes for many people. Work is being done on fixing it, but no one quite knows why it causes crashes so progress is slow.
#7 is looking popular I guess. The damned daedric axe icon for auto-cast spells is svcking.
7. Better kind of icon support especially for Auto-cast keys would be nice.
9. Some items (like Alchemy stuff) doesn't need to be in your inventory all the time, but would be really good if hotkey remembered it when it's put back. Not a major hassle to rebind, just a -would be nice- one

#7 is looking quite popular I guess.
9 is easy.
If you're still looking for testers, I'd like to try modified .dll! Things have been hectic IRL these days. :ahhh:
My requests:
Aforementioned Flexible Keymapping with .ini settings (V, B.., F1, F2.., Num1, Num2.., etc)
Cycle Potion/Poison Selector Hotkey
Poison Coating Hotkey without Confirmation Message (acts like Potion Drinker Hotkey)
Take Everything Hotkey in Looting Menu
Customizable Console Command Hotkey with .ini settings (tg, tdt, tfc, tgm, tcl.., etc)
Spell Delete Hotkey
I've sent you a PM with a link to the dll.
This mod is not likely to do Spell Delete or Take Everything - its hotkeys are not really intended for use in menus.
I might do a seperate mod for Spell Delete however, since scruggs Spell Delete seems to be the only standalone spell delete mod and it clearly has room for improvement.
I would do a seperate take everything key mod, but I don't know how. I've made requests for such a mod before.
What would a cycler potion/poison selector key do? Act as a cycler key that merely switches potion/poison type for the virtual actively-selected-potion thingy of potion select hotkeys? I could modify the existing potion selector hotkey type to be able to be bound to multiple potions and cycle through them.
I can modify potion drinker keys to support poisons too (if they don't already, I haven't tested that), or modify all hotkey types that select poisons to suppress the the confirmation box (if they don't already, I haven't tested that).
A customizable console command type hotkey is certainly possible. It sounds kind of weird, but conceivably an in-game text entry box could come up and allow you to type in scripts to be attached to a key.