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.
Bitmessage isn't attack resistant whether or not it is used over Tor... As for your suggestion of a "proof-of-publication side chain", as always, it's a matter of security vs. cost. Just using Bitcoin itself gives you high security at relatively high cost. (though potentially not as high as you'd expect giving the complexity and inconvenience of getting coins to pay for a side-chain)
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...
Again, we're talking about proof-of-publication here, not data storage. As I suggested above, think through how the idea could be applied to announce/commit sacrifices.