I think the ideal scenario would be building it on top of or alongside Stack Overflow, not separate from it. Their network effects are incredibly powerful, if they were willing to add lightning payments I think it would be a huge success for everyone involved.
A potential workaround solution could be building some kind of browser extension that would work on top of Stack Overflow. You can ⚡ tip the question answerer, and then they are DM'd that they have received a lighting payment if they set up an account with the service.
