Even if people aren't scraping the network to record the order of block creation, it will be mighty suspicious when the Y blocks are scattered randomly across the network, and the Z blocks are conveniently hosted in one place.
> Even if people aren't scraping the network to record the order of block creation
I'm not sure if "scraping the network" is possible if chunks have unguessable names. Also, it's possible that someone could have a file shared among friends (over TLS), for years, without it being publicly announced.
> it will be mighty suspicious when the Y blocks are scattered randomly across the network, and the Z blocks are conveniently hosted in one place.
I suppose it depends on how blocks are distributed in the system. If the blocks of Y are all served from y.com and you host your Z blocks on z.com, then both hosts will look equally suspicious is Y XOR Z produces an infringing file X. The owner of z.com just needs to be able to credibly claim that y2.com was already hosting the Y2 that XORs with Z to produce a legitimate file.
Alternatively, a single node could host Z, Y, and Y2, all created by users, with no logs kept of when each block was created or requested (and no search/listing function). Such wilful ignorance may not impress a court, but is roughly equivalent to running a non-logging VPN, or a chat service that doesn't retain metadata, or a Tor node, or an online encrypted backup service. The service could even offer to follow a DMCA takedown procedure, in case non-XORed non-encrypted blocks were stored on it.
