Hello, I'm Chad, TheSaltyPug, and I'm here to propose an idea!
I like the standard inventory that Minecraft has, but it should have an overhaul! I've always loved the idea of having to equip armor to have more slots. I was thinking that there should be a mod that gives more slots based on the kind of armor you have (or to make it work with other mods, the amount of armor points it gives). For example: equipping a leather chest plate might give you 9 extra slots, but a leather one would only give you 2. Similarly, with leggings, you can have extra slots with an increasing amount depending on how good the Armour is. It probably should not work with boots or helmets.
This could potentially work with other armor mods too, if it is coded to work off of the amount of armor it gives rather than the armor itself.