there are things I didn’t realize when writing the OP. I think the general state of affairs is worse than I thought:
-
I didn’t realize resources can be abused to such a degree in Zcash. if a simple transaction and a 1 MB transaction both costs 0.0001 ZEC, and let’s assume 1 MB the biggest transaction that’s feasible to create, then filling all block space costs just ~$15/day. basically it doesn’t matter if it’s a single programmer having fun or the World Economic Forum making sure you’ll own nothing and you’ll be happy, anyone can make the chain unusable at their will. that’s a big problem.
-
doing it through shielded transactions publicly demonstrates that anonymity sets in Zcash can be inflated/poisoned without substantial costs. by “inflating” I mean that they can make the set look big, which influences users’ assumptions about their level of anonymity. e.g. you think that the potential inputs for your transaction are 10,000 previous outputs, while they know which 9,900 outputs were created by themselves and the number of real potential origins is just 100. the poisoning aspect is mostly the same, but affects those who want to gain obfuscation by shielding ZEC, keeping it in the shielded pool, and then unshielding. these users will also be misled about the true size of the anonymity set (the number or organic shieldings or unshieldings to/from a shielded pool).
-
if this continues in a sustained manner, then yes, as @hanh suggests, this would require a hard fork. doing this spamming 2 weeks after a hard fork seems to be a malicious timing.
@d3l so it seems that the spamming is the spillover of some conflict within the Electric Coin Company? it’s quite ironic then that @zooko even retweeted the transaction increase graph 
here are some other messages as vanity addresses: x.com
not if the fee is not defined as a constant/transaction (see fee structures that make sense below).
it’s not really, and it does reflect badly. block space is a scarce resource in any decentralized blockchain, and the way you protect a chain from resource abuse is to have proper resource pricing mechanisms. without that, a blockchain’s resources can be abused and the chain made unusable (effectively censored).
I’m honestly shocked to read this from someone as smart as you and who works as a scientist on a public blockchain. why do you hold this view?
a proper fee mechanism is not a 100% guarantee that you won’t get spam, but it almost always ends up being effective because of the economic reality: requiring a sufficiently scarce resource in exchange for another one (the “almost” refers to heavily funded adversaries with extra-protocol incentives). Bitcoin requires you to pay for data written into the blockchain and allowing a first-price auction of the fee rate between participants. Monero does the same but lowers the fee rate as blocks get bigger. Ethereum is somewhat similar too, but you pay for unit of computation and there’s a minimum required fee rate that is the function of how full recent block were (I’m simplifying). these are just the most obvious fee mechanisms and these chains have been quite resilient against spam attacks for a long while. you could argue that transacting on them hasn’t always been the cheapest, but that’s simply the price of having censorship-resistance, and if you want cheaper transactions, there are various parameters to tweak in sensible fee mechanisms (there are many more beyond my list) to achieve that. but charging a static fee per transaction is just crazy, sounds like an ill-conceived strategy to market the chain as having cheap transactions. (proof: almost none of the pages on z.cash and electriccoin.co can resist the compulsion to mention it.)
saying that faster Orchard verification will solve this is pure copium, that doesn’t take the system’s general availability and node storage requirements into account at all. not to mention it looks like it’s at least as cheap to spam the chain with fully transparent transactions as with fully shielded Orchard ones.