A nonprofit overseeing a for-profit arm, where have I seen this before?

Plenty of places -- it's not an especially rare model.

Yes it is common for a charity to own a business. The corporate profits are used to fund the education or social welfare mission.

I think it was a dig at OpenAI

Mozilla and OpenAI.

Novo Nordisk would be the biggest example I'm aware of

BBC Studios / BBC America

Mozilla

IKEA?

Same thought I had, though it seems more like a tax-dodge for IKEA: https://en.wikipedia.org/wiki/IKEA#Financial_information

TIL Ikea is technically non-profit.

That’s insane

The NFL used to be a non-profit with the teams paying tax on their profits. It's since changed.

(silently acknowledges that this is a rhetorical question rather than a brainstorming prompt)

Rolex? They take $10 of cheap metal, sell it for $10k, and use the profits to fund the charity.

Sounds like OpenAI

How much de facto control will they have left after selling all these shares though?

Because despite the a slight shift in political tone, making profits on HN is still hugely unpopular. Even if it is a for profit under a Non-profit Foundation.