I recommend to adapt an existing open source affiliate wordpress plugin by extending it with Bitcoin pay/payout feature. Developing it from scratch and market it as premium will not be profitable. The market is just too less in order to find an critical amount of paying customers.
Agree. One plugin with all common processors extended with bitcoins is better.
I just realized there is no reason for this thread to exist. Wordpress.org list dozens of highly-maintained plugins with big active install counts that support multiple crypto coins along with fiat gateways like Netseller and PayPal IPN.. Complete with back-end management.. Free..
If you made one it'd have to have better security and efficiency else nobody would care.. No money to be made and no solution to provide that isn't saturated..