> To what extent is MSE reputation an indication of potential in academia?

Very little. You get a lot of reputation for [simple answers to simple questions](https://cs.stackexchange.com/a/61024/9550) that make it onto the HNQ list, because those are the ones that people can quickly understand and say, "Yeah, that's right." Conversely, you get little reputation for deep, [detailed answers to difficult questions](https://cs.stackexchange.com/a/79720/9550), because people can't be bothered reading them.

High reputation on a technical Stack Exchange site might indicate that you're a good teacher of that subject, since well-explained, easy-to-understand answers tend to get higher reputation. But, the teaching experience you get as a student and early-career researcher will be a much better indication of that.