Here's an option to reduce the risk of a single entity controlling all of XBTC causing systemic risk. How about I transfer XBTC to the developers and they by enrolment allocate portions of the XBTC to entities who wish to underwrite the value of XBTC to BTC. The more the better. That way, if any single entitty was to do a 'runner' it would have a reduced impact to the value of XBTC.
In such case, we need 100+ underwriters, I think.
In a situation like this each underwriter/backer can accept and exchange each others XBTC and BTC. There could still be room for Poloniex or another one or two larger more liquid underwriters to act as clearing houses for all the smaller underwriters.
I think there is only 1 way to perfectly implement this pegged value idea. Create a DAC (Distributed Autonomous Community) whose sole function is to take an amount of BTC as an input and return the same amount of XBTC to you in return. This DAC will run on at least all the underwriters computers. This keeps it as simple as possible. The DAC is trust-less and starts with the 21 Million XBTC. To get the XBTC you have to feed it with BTC. All the accounts would be transparent and really simple - only 1 address is needed for both the BTC and XCP.
This would work for any other crypto-currency too. The only caveat being that the members of the DAC community would have to run the blockchains of each cryptocurrency involved.