A CT-style system could work for supply chains, but let's say for the sake of convenience, we wanted to use some shared storage system rather than building a ne

A CT-style system could work for supply chains, but let's say for the sake of convenience, we wanted to use some shared storage system rather than building a new system for supply chains only. We could have one big CT-style log system host many applications, but as the number of participants grew, we would want some mechanism to prevent spam. Even if there was no outright spam, some users would generate a large volume of logs with questionable utility, and humans would need to get together to decide if those users should be blacklisted or what. Ethereum gives us spam control via gas costs. I can't imagine a good, low-maintenance solution that doesn't resemble some cryptocurrency. Paying fees from a ledger isn't absolutely necessary -- we could proof of work to discourage spam, like iota -- but charging fees in a ledger seems like the better solution, and isn't that much more complicated.