I view Memo as a nice proof-of-concept, but long form / high volume storage will be better served by other blockchains or solutions long term, and then this tech will fade out. My 2c.
Perhaps multiple blockchains is the way things will go, but to me a single chain seems more likely.
I actually tried the "multiple blockchains" strategy with data in mind. It introduces more attack vectors than just IPFS. It might work in some cases tho.
Maybe we need a way to incentive archival nodes. If eventually there's a lot of data, we could develop something like swarm nodes: parts of the blockchain stored in multiple nodes.