Correct. I was too specific but it only because I am playing with vanilla grenades.
What about having Ctrl-Click on a grenade to arm and equip it in hand from the inventory screen.
It still requires entering and exiting inventory. So no much of a save. Although, if this is possible, I'd take this too. At least some click reduction.
However, if Ctrl-click can be programed, so the configurable keyboard shortcut, I guess. And then modders can hook different item types on it as they see fit. I don't think we need more than 3 shortcuts max: smoke/dye, flare, grenade. Configurable for other mods to substitute items there.
The "grenade" shortcut can include the list of items those will be picked in order or existence. If first one is not there, look for next type, etc. I believe it is absolutely enough. No need to complicate things.