I think this introduces more user friction, at least without some kind of built-in DEX for the user to buy NAM if they don’t already have it – we really want to support users who just want to shield or unshield other assets (but are willing to pay a bit of a fee to do so).
This proposal is intentionally non-committal about what we do with the fees, I think that decision can be made separately – some relevant discussions can be found here. Personally, I think perhaps a combination of maintaining a treasury balance in other assets, providing protocol-owned liquidity and collecting fees, and buying-back NAM could make sense.
If you’re looking for more liquidity or the ability for the network to perform market operations, I think that this fee system could be quite synergistic: collected fees could be used, for example, to provide protocol-owned liquidity which would help stabilize markets over time. I’ve been working (along with some researchers) on a design for a metastability mechanism which I think Namada could deploy a first version of if there’s interest.