You'll need some mechanism to raise rates to attract top developers.
Even without the first free minute and time spent reading questions, the most a dev could hope to earn with this service is ($0.75/min)(60 min/hr) = $45/hr. Perhaps for students or devs who barely meet the 100 rep minimum requirement, that might be attractive, but for the experts who've written the best Stack Overflow answers, that's likely to be a (small) fraction of their bill rate.
Free contribution is rewarding as a means of helping.
Well-paid contribution is rewarding for the $$$.
Poorly paid contribution often loses both incentives.
Even without the first free minute and time spent reading questions, the most a dev could hope to earn with this service is ($0.75/min)(60 min/hr) = $45/hr. Perhaps for students or devs who barely meet the 100 rep minimum requirement, that might be attractive, but for the experts who've written the best Stack Overflow answers, that's likely to be a (small) fraction of their bill rate.
Free contribution is rewarding as a means of helping.
Well-paid contribution is rewarding for the $$$.
Poorly paid contribution often loses both incentives.