On the system level:tax the billionaire?

1. Found a unicorn. Congratulations!

2. Get a tax bill

3. Either loan against your shares (good luck) or(and probably even if you do get a loan)

4. Go public early, selling your shares and let others partake in the companies growth

Alternatively, give your shares to employees, donate, whatever. It's not really rocket science, just tax wealth (radical markets proposes a nice way to get honest self assessments...) and as a side benefit, you benefit employees by creating much more incentive against staying private forever