Wasn’t one of the most driving factors for Halo, to make the Zcash protocol more capable of upgrading on shorter cycles?
Just for clarity, Halo2 allows us to make upgrades to the ZK circuit without having to perform a new trusted setup ceremony. So for example, the upgrade to adopt ZSAs can be made in a normal hard-forking upgrade. This doesn’t have a lot of relevance to changing purely-transparent parts of the protocol.
The issue with protocol-enforced “super transparent” addresses, as I see it, is that the “super transparent” concept solves a made-up problem: if a user transfers balance from their shielded pool to a fresh transparent address, and then transfers that balance to a “super transparent” Binance address, the only thing that Binance has gained is the ability to return funds to the originating transparent address. That’s a very small gain, and @hanh’s proposal provides the same benefits at a much lower cost.
Protocol upgrades aren’t cheap; there’s implementation complexity and risk involved in any change to the consensus rules, and then there are all the knock-on effects on the wallet ecosystem, where wallets must update to accommodate new transaction formats. I mean, heck, the problems with Ledger hardware wallets today exist because as far as I’m able to tell, Ledger never implemented support for the V5 transaction format (or at least not V5 transaction signatures, it’s hard to tell.) If Zcash developers are spending time implementing this sort of feature (which regulators might come back and say is inadequate anyway) then that takes time away from working on everything else that needs to be done.
Privacy is a fundamental human right, but just as importantly you can’t actually run an economy on a fully-transparent coin where everyone’s paycheck, every business supply chain payment, every doctor’s visit is ultimately public information; you can’t run an economy on a chain where miners or notaries can arbitrarily discriminate against certain transactions. I want zcash to be the chain that the economy runs on; we’re the only one with the features needed to actually make that happen.