I'm not convinced it'd work. Not to be mean at all, just realistic. The huge bulk of this tax bill was from exercising stock options. According to another co

I'm not convinced it'd work. Not to be mean at all, just realistic. The huge bulk of this tax bill was from exercising stock options. According to another commenter here, 44% on $1.34B earnings from these options. So given a $1.5M cap, these options simply wouldn't have been exercised. You'd use your options up to the $1.5m earnings ceiling, and then stop. So the tax 'purse' would receive the pre-ceiling rate on $1.5M instead of 44% of $1.34B. A 100% ceiling sounds very straightforward, but the end result would have been that Musk would have paid over $592M less in taxes over the same period - and I'm pretty sure that wasn't your intent. (sidenote: With regards to the morality - under your proposal, the Bill & Melinda Gates Foundation wouldn't exist. I think I'd rather any proposal allowed for such altruism.)