We're talking about network-level sybil attackers; this isn't about hashing power.
That is what I'm talking about. How do you know if your view of the network is being constrained? By comparing with the most recent prices on the chain. Of course this is defense in depth as you'd also be using network-attack resistant networks like a bitmessage over tor and a proof-of-publication side chain for distributing orders.
We'd have to wait for an actual P2SH^2 implementation.
But from the P2SH^2 discussion, it looks like the data would be relayed/published along with the P2SH^2 even though it will not be not stored.
No, only the intermediate hash.
How do you know that hash is a hash?
What does that matter? You've proved that the data on the chain is a hash, not arbitrary data. At this point I think we're talking past each other...