100% agree that the bigger the problem scope, the harder it is, but then a big problem scope is itself a problem. I think bounties for github issues are a much better way to do these incentives, as the scope is usually much smaller. And if the issue is of a big scope then you can just create another smaller-scope issue and attach bounty to that one. 

 It was a little disappointing, the person that was trying to do this already, had hired someone to do it.. but they couldn't do it.  From what I could tell, they got hung up on the implementation details and it got more and more complicated .. similar to what mazin was saying.. there is a branch somewhere with where they left off.