I like the idea and I've previously pondered something similar. It'd be sort of like the way you can put a bounty on StackExchange.
We potentially end up with people not paying, and dealing with an escrow is beyond the scope of this site (in my opinion).
There's nothing stopping someone from using a VPN and just signing up for new accounts. They can just stop using their account and never pay but still ask additional questions.
Then, we have non-concrete answers. In other words, we have incomplete answers where it takes more than one answer to really reach a solution.
Then there's the temptation some may feel to just guess at solutions, filling the thread with less-than-good responses and increasing cruft. Some folks, probably those with less money, may start 'shotgunning' the thread with possible solutions, especially when word gets out that they can make money answering questions here.
Things like that make it a potential problem. Those are the things I think about.
But, I am interested to see where the thread goes. Like I said, I've pondered this before - though not by that name, even though I'm familiar with StackExchange.