How funny it was to read this post 13 years later
Reminds me of the story about buying a pizza for 10,000 BTC, now worth $515 million.
While there are parallels with Laszlo's Pizza Purchase from around 15 years ago, the main reason as to the main reason why OP's pushing for the big mac index is to further push the idea that bitcoin is for the people. If that even makes sense. When you get into the big mac index, it would automatically mean that the currency you're using is either socially-accepted as a full-fledged currency to be used for daily purchases, or at the very least, a legal tender that could be used as regular money for purchases.
There is massive implications and benefits to this as getting bitcoin or any cryptocurrency for that matter further solidifies the notion that cryptocurrency, is just money glorified and given new features. Which many people believe it not to be all because it's not tangible or whatever. By allowing people to realize that while they can earn money through bitcoin and crypto, they could also use it just as their regular crumpled dollars or pesos, it would allow for a heightened chance at getting bitcoin to be accepted by the public which has been one of the biggest barriers towards global adoption for so long.
My only reservations about this plan is honestly the fact that there's a lot of discussion to be had about the territorial and governmental aspect of currency, and since bitcoin's decentralized there's going to be a lot of discrepancies surrounding that.
