I guess you could ask witnesses to host such nodes. They already kind of have to host a seed node, why not ask an IPFS node from them too? At the moment, the pay largely compensates for it. More generally, I believe that a network supporting a DAO will need various types of specialized nodes to efficiently provide the functionality offered by the DAO, and this should be payed by the network itself. We already have witness nodes, seed nodes, now IPFS nodes, I can see more popping up in the future. I'm sure we can find a way to pay for all of them while avoiding abuse / theft of funds at the same time.