I really would like bag-friendly VIP storage to be a thing too. Honestly if you're worried about accessing/removing items from bags in VIP, I have a couple suggestions:
1. like normal VIP, the bags should act like a one-way bank for any items when you're no longer a VIP player - so if you need something, you should still be able to open/access the bags, but you just can't put anything back in. Also, for safety, bags can't be removed from VIP unless emptied, to avoid being forced to drop or hold them in your mouse until you figure something out.
In this system, when VIP expires:
-bags can be opened
-bags cannot be removed from VIP tab unless emptied
-bag inventory is greyed out
-you cannot use items stored in bags
-you can remove items from bags, but cannot put items into bags
2. If this isn't possible due to some weirdness with Mabi's engine, then bags could instead act more like the shop kiosk stalls - you can't directly access them when VIP is expired, but you can 'clean' them and remove all items in each bag when they're inaccessible (basically this is pretty much just adding a 'clean bag' option to the right-click menu for all bags). And ditto on the 'safety' thing.
In this system, when VIP expires:
-bags cannot be opened
-bags cannot be removed from VIP tab unless emptied
-you can choose to 'clean' the bag, emptying the bags' contents into your regular and temporary inventory space