I don't know how you can have both censorship and censorship resistance in an immutable database.
In fact I wonder if it's possible to have censorship at all. Even if there are no fields for arbitrary user data, it'd be possible to encode data in the amount field.
What would a bank or stock exchange do if they found out illegal data is encoded in their databases through a sequence of stock market prices? Roll back all the transactions?
I'm afraid, if ZenPub will not have any censorship, it will become a trashcan with child porn and nazi manifests. And all ZEN block chain will be banned by officials. So, maybe, it will be rational to refuse from ZenPub file storage at all. You should never underestimate humans stupidity, which can destroy any new brilliant technology.
I share the same concerns, something we'll seriously consider before releasing design specs. It's possible to consider a gatekeeping function where maybe the community has a veto function before committing to chain, but even that raises questions.