I'm sorry I don't read your last post as such. Let me know if the following is indeed what you had in mind.

P2P pairing of asks/bids is trivial as you noted.
Now you're talking about an analog currency counterpart to a btc order, and use of an escrow to validate it.

If the 2nd currency is also a block chain, then there's no need for a trust artefact.
Nodes are paired, 1 transaction is made for each currency, that's it: pairing is really all you need technically.

Now the problem is how does that 2nd currency trades against analog resources. If it's got the same characteristics, then there's good chance both currencies will get completely paired in real time, you're left with 2 clones of the same thing and you haven't moved any closer to analog value.

There are IMHO 2 solutions out of this:

• Either the 2nd currency must have another intrinsic use and value (namecoin is actually maybe a good candidate), so that the market can indeed value them differently over time
• Change the dynamics of the 2nd currency. You can for instance  imagine that initially, the P2P Exchange is also a bank that collectively owns all the available bt$ for that 2nd currency with no more mining allowed.
  
  • Once the exchange is already up and running, one can join the exchange simply by starting to trade btc for bt$, either with an individual or with "the bank", which always trades at the last ticker price.
  • The only way out is by cashing out your bt$ into btc either from an individual or from the bank.
  • The main question is at the beginning then: who creates the bank? Whoever does so could in theory accumulate a large quantity of bt$ for nearly no coins and we get back to the arguments about Satoshi Nakamoto and early adopters. One could also decide that for a period of time, bt$ will trade for a fixed rate of btc until the bank reaches a good reserve of btc. That leaves time for everyone to get in at identical conditions. Then only can the rate vary according to free market.
  • If the bank gets dry, it means someone it means people have cached out the initial amount, which could be a problem since it means bt$ are again left paired with btc until the bank can warrant withdrawals again. One could say that in such conditions the bank keeps a reserve of BTC, an insurance built over time with transaction fees for instance, and maybe a period of controlled rate, with the acceptance that moderate withdrawal at market price is all you are guarantied -> this is pretty much MtGox conditions as we know them and this is probably fine with most btc users.

What do you guys think?