Scottish Mortgage (SMT) in the UK does this and has a stake in Stripe (https://citywire.co.uk/investment-trust-insider/news/boost-f...)

This is already a thing, large investors like Fidelity do exactly this.

e.g. Fidelity has a significant investment in SpaceX through a handful of their mutual funds, which you can then purchase and basically invest in SpaceX indirectly.

Publicly traded organizations can have any kind of private investment. I wonder, though, if there is regulation around how much of the public org’s capital can be put in private stock purchases…

I think some VCs are already also offering shares via mutual funds.