I can picture this working, actually. Someone could put some smart contracts into the Ethereum blockchain, for example, one per piece of software, with the instruction that if the contract receives more than a certain threshold in total donations, a transaction is sent to a CA asking them to issue a code signing cert to the developer of the relevant piece of software (hardcoded into the smart contract).

The CA would have to be in on this, by having an Ethereum address to receive the crowd-funded amount at, and they would have to make contact with the developer and verify them using their normal methods, but there would be a strong financial incentive for them persuade the developer to accept their certificate. Perhaps if the developer declines, then the funds controlled by the smart contract can expire and be sent back to the unsuccessful crowd-funders.