It's not a bad idea at all... but it would most likely take some of bitcoin players to contribute to this.   Let's say one of the exchanges waives all fees to convert the donated coins to USD for them then it's something that would get them press and allow for wikipedia to collect USD from bitcoins.

I'd be willing to make it easier for them to get donations... flexcoin id : wikipedia for example

but the converting to USD has to be though an exchange.