First a little of context:
I love the game mechanics around Quark's backpack where you have to choose between your armor, wings or backpack (even if it doesn't make sense, common you can def wear a backpack with armor).
I hate "end game armors" that put everything in a convenient space for just convenience (looking at you rise & shine).
BUT I also like my sanity.
As for now, there's 2 modes for the backpacks:
1.- you're locked with a backpack in your chest slot while there's any item in the backpack
2.- you enable Super Op Mode and get your backpack as a shulker box with extra steps
My suggestion is a middle point, allow to swap the backpack with armor/elytra on a armor stand
the desirable use would be, you have a backpack with your tools, right click the armor stand that has the armor you want to wear next and it's swapped with your backpack without dropping the items. If you break the armor stand that has a backpack with items in it, it will drop the items inside the backpack like it would do from the player.
Sometimes when you're building something and want to take a break to, for example, go to your pickle farm to pick pickles, that's 2000 blocks in the ocean, you'll want an elytra and you won't need all the tools and block you were storing in the backpack a this moment. In the current scenario, you'll have to dump everything on a chest, swap your backpack with the elytra and reverse this when you're back.
My suggestion also gives the colored backpack more use, now a colored backpack is just a design choice, you don't have a pink backpack for building, a black one for picking flowers and a blue one for commuting with pigs (unless Super Op Mode is enable of course), but having the option to have a wardrobe with a few armor stands with colored backpacks filled with the tools you will need for the desirable activity would not only be useful, but also cool.
Would this have a way to abuse the backpacks?
Yes, armor stands are entities at the end of the day and you can easily move them. But I'll argue that's not more effort than just moving chests, and if someone goes to the effort to make a way to have multiple armor stands with backpacks following them just to swap em on the way, I'll say they deserve the extra slots.
tl;dr: read the bold text.