How would you balance difficulty though? Altepa T2 VNM can be soloed, and once you upgraded once to T3, free and indefinitely. Where most others require expensive pop items (and sometimes pop items to pop NMs that drop pop items.)
Or to put it simple... how many PUP body seals for a single RDM body seal? 3? 9? 30?
Even if SE added a swap option, it would be something like a once-a-game-day 3-to-1 trade for a random seal of the same type. So you can take 3 PUP body seals, and get 1 BST body seal in return.
SE only added quivers for a few arrows and bolts. They should have done it for ALL of them. It killed the market for higher level arrows like Gold and Platinum because they won't quiver.