What type of fee mechanism do you think could ensure that ZSAs don’t artificially multiply the value of the Zcash network but generate no where similar demand for ZEC?
Or that freeloaders won’t be abusing the Zcash network because they can shield assets for an insignificant fraction of the asset’s value in ZEC fees?
If we can’t solve those two things, then thinking ZSA’s will be part of a “virtuous circle of growth” for ZEC is just not really backed by anything.
Transaction fees don’t depend on the ZEC value transferred in a transaction. They can’t for fully shielded transactions, because the value is private, and they don’t for other transactions. This is fine because the cost to the network isn’t dependent on the value. Why should transactions involving ZSAs be any different? (Because ZEC actions and ZSA actions are indistinguishable for a given tx version, they can’t be without unnecessarily leaking information, anyway.)
Transaction fees are only there to discourage denial-of-service and to incentivize inclusion of transactions in blocks. They’re not like fees for a credit card, which are a rent-seeking mechanism to extract as much from the user and merchant as they will bear.
Granted, there is limited transaction bandwidth and use of ZSAs will take up some of that bandwidth. The case where they take up a significant proportion of it is the case where ZSAs have been successful and enjoy widespread use. We shouldn’t be worried about that per se, as long as we have proposals that are likely to be able to significantly increase transaction bandwidth in the necessary timescale, which we do and that are needed with or without ZSAs (Tachyon).