Regarding your first reason, I think having more users can increase the security of the data, even if you're conservative about the minimum number of users you

Regarding your first reason, I think having more users can increase the security of the data, even if you're conservative about the minimum number of users you need. For the second, if you don't care about data permanence, it's relatively easy to put the data on a second layer. Just host the data there and put merkle roots on the blockchain for consensus. If you want to verify state transitions on chain you can do that too, e.g. with zksnarks.