FOSS gamedev and creative worlds

My answer to my own question is “Yes”.
Rationale:

Bags are a gameplay feature, and a pretty heavy one, too. They add up to 96 inventory slots, which is a lot compared to the original 32 slots you have at the beginning.
I see Unified Inventory as a convenience mod which is supposed to enhance usability, and I see bags as a heavyweight gameplay change. Therefore, Unified Inventory conflates both gameplay with convenience feature, you get two features at the price of one (even if you only wanted the inventory) if you install Unified Inventory.

If the bags are instead in a separate mod, it is easily possible to only get the “pure” inventory enhancement without any gameplay changes, and those who want the bags can of course still get them.

I have nothing against bags themselves, I just don't think they should be conflated with an inventory mod. To me, adding bags in the Unified Inventory mod is like all players get healed every second because you have a crafting guide mod installed. It just feels off. ;-)