I understand what you're saying. The only problem is what data is in that decentralized, available, secure data store. The only data allowed in is self-referencing data. Most people don't care about the Bitcoin data store. If I could access, say, Gutenberg.org books in that data store, or something of that nature, I and others would find more value in it.

On the other end of that, processing, not data, there are distributed processing projects out there finding the optimal golomb rulers, looking for pulsars, how protein folds etc. There could be value in a distributed project processing these and other projects. All of Bitcoin processing is self-referential though, it does not allow for this potentially more valuable processing.

What you're describing would be valuable, but not if the only data storable is self-referencing. People don't buy 1 terabyte disk drives that already store Bitcoin blockchain history. They pay for hard drives because they will store the information they want to store and retrieve on them.