Anyone can make a public read-only share of their files, including blockchains. This would be useful to bootstrap your node from a trusted source (say, a day/week old to ensure consensus was successfully reached).
I wouldn’t recommend a public read/write share though, as it wouldn’t be a reliable mechanism to append to the blockchain. I would suggest people just write to their own copy and allow de-duplication to work its magic.
Ofc, this is all for non-native clients, which just need file system access. There is a whole separate debate over whether transaction sequences can be created natively using the REST API to write structured data types directly. We had a great debate about that here: Public Ledgers and Proof of Transparency on SAFE