option to pay developers for feature/bug fix

It would be nice to pay directly to software developers for features or bug fixes. A lot of times I heard that people using some software complaining that something is not fixed or feature still not implemented and they are even ready to pay a little for that, some people even say "stop improving this dolphin, fix my monitor auto-detection I will give you $100". Right now we have donations as a "thank you" after something is done, which is very close but not yet ideal.
Cooperated users should be able to buy features and good open source projects should be able to provide more or less adequate price for the implementation.

Launchpad itself may provide a way for users to "vote" for features/bugs using cash and project teams to setup their accounts and distribute earnings.

Thank you.