Yes. I imagine this has been heard before ... but I've got my favorite beating stick, and I can't resist a dead horse when it's looking me in the eyes. So let's begin:
I get it. I really get it. I promise. You want me to buy the gigantic bags in cash shop. But making the vendor-bought bags exclusive isn't doing that. Instead, you have me doing gymnastics with my vault, my shared storage, and my inventory,trying to arrange collectables. And it's an unnecessary headache.
When I go to the grocery store, they aren't telling me "Sir -- Sir! It is physically impossible for you to carry two Stater's Bros. bags at the same time. You've got to trade one of those out for a Vons bag immediately!"
I don't think the store-bought virtue of having all collectables (ingredients, ect) in one inventory slot would be superseded if you let me carry my 3 collectables bags in my inventory, so I didn't have to juggle. Just some food for thought.