ISOs have a 100k cap per year.
Further, the next line after your exceprt is "However, you may be subject to alternative minimum tax in the year you exercise an ISO", which is an income tax
He did not get some custom stock now that will appreciate in value magically, if and only if he meets targets - or certain types of options can also act like this.
Even if GOOG stock grew so much, that this ended up being a $3B pay package, he'd be taxed as ordinary income on the full amount at payout - not even the reduced capital gains on the extra ~$2.7B in growth between agreement and payout.
It sounds like you're describing a hypothetical tax on unrealized gains? Do you have a link to the Buffet letter?
This may assume that there is more alpha in the shares than other investments you have access to, which is perhaps less true today. But it should probably be your position if you're CEO of the company...
All the Buffett letters are online, but I don't remember what year it was. If I get time I may find it and report back.
If you want to research the tax imlications, the relevant term is PSU (Performance Stock Units), which is the form almost all of these CEO incentives take.
I'm fairly sure that Sundar Pinchai will have paid someone to research the tax implications before negotiating this deal.
Why do you think that?
If you sell them immediately, then you don't pay any additional capital gains tax, because there were no capital gains from the moment you got them to the moment you sold them.
If you hold on to them, you will eventually pay capital gains on any increase in value from the moment they vested until the moment you sell them.
Perhaps, once they are vested, you could take loans against them, to get some cash while avoiding selling them.
But no matter what, they are taxed at the moment you receive them, and again at the moment they leave your possession.