I'm a Quaker, and actually, it's not thou at all. It's always thee. Somewhere fairly early on, the grammar was totally altered. So it'd be stuff like "What does thee think?" and "Has thee anything to add?" I've never actually used it. I only know a few people who do, and even then it's only occasionally, to emphasize something as being Quakerly. Which means, yes, formal or technical, or sometimes just passive-agressive. Some people do use it as more familiar form. It's only the rare, rare people who do plain speech and use it with everyone.

Ahh, language.