IMHO, the "weak point" of Futarchy is the 'goal metric'.
In corporate governance ("Fire the CEO" as advocated by Hanson), the stock price is the goal metric. This is convenient because the spot price of a corporation's stock is itself resistant to manipulation (the dividend payments, and market for loanable funds, should keep it in lockstep with the market value of the assets of the corporation). A parallel metric for a non-profit might be some metric set by its board of trustees, or by a nation's voters, but this metric would probably not be resistant to manipulation. In the business world, you can't fake what you've produced: it's either there (to take home to your family, or sell) or it's not. Advocates of Futarchy mention GDP, leisure, education, inequality, and health.
GDP (PPP) per capita is a highly reliable indicator of national welfare....today. However, if we adopted GDP/Pop as our 'goal metric', the reliability might plummet. Futarchy would demand that we adopt the policies which increase pc GDP as measured by X
, so it is likely easiest for a tyrant to go straight for X, and through that, seize control of the nation's policies and the nation itself.
Most other ideas seem open to Sybil attacks. The best idea I have so far is:
1] Have every Bitcoin (or CashCoin) account sign a message answering: "From 0 to 20, how satisfied are you with your government?"
2] Average the satisfaction numbers, with the BTC balance as weights.
We can have several different metrics ("...how satisfied are you with respect to 'educational availability', or "your health").
The most obvious problem is that: This is a plutocracy (the government is doing whatever the wealthy want [some consider this a "pro" instead of a "con"]). A second obvious problem is that this is self-report (you can have a terrible educational outcome, but lie or exaggerate your experience), which is why I bite the bullet and ask something directly subjective ("how satisfied are you").
To solve problem 1, we might try something like this: http://www.ted.com/talks/david_bismark_e_voting_without_fraud?language=en
 n = nations_population (quantity of ballots)
 Cryptographic set up of 'the vote' (on this day, this many keypairs, this voter-eligibility).
 Go to election HQ on election day, randomly select your sheet with a keypair.
 Go home to Namecoin, use your keypair to extract the "ballot form", use it to cast your votes.
 Check the outcomes after the fact.
I have no idea how to solve the second (self-report) problem.
Does anyone have any ideas in general, about how to reliably measure a nation's success?