Yes, please, on wearable containers actually containing items, rather than just adding more hammerspace around your body.
On implementing the interactions between mutations and clothing, I’m not convinced an elegant solution would be hard to discover.
Of course, I consider the implementation of a snipe-ton of item tags a sufficiently elegant solution. Your standards may be higher.
Example:
Item tag: COVERS_FINGERS
Valid only for items that occupy the Hands slot.
Attack tag: REQUIRES_UNCOVERED_FINGERS
Tag is attached to claw attacks.
Code that determines which attacks are currently valid must return false for an attack that REQUIRES_FINGERS if character is wearing an item that REQUIRES_UNCOVERED_FINGERS.
That’s two tags and one line of code.
Another example:
Item recipe tag: SCALABLE_WHEN_CRAFTED
Item tag: SCALED
Additional line of code for crafting: If the player is too big for his britches, a SCALABLE_WHEN_CRAFTED recipes produce a SCALED item.
Additional line of code for wearing items: Oversized player can wear an item that is SCALED.
That’s two tags and two lines of code. Maybe you need another tag for mutations (REQUIRES_SCALED_ITEMS)–I don’t know if size is kept as a separate stat.
The set of mutation interactions that can be handled this way is large enough to achieve quite a bit.
Any interaction that can’t be handled with a few tags and an additional line of code in one or two places gets put in the parking lot.