At the very minimum, I can already see every university and high school student paying for GPT-4. Its a way way way more powerful essay writer and personal tutor than GPT3.5, that alone is incentive to upgrade. For only $20 a month.
Know what GPT-4 currently is insanely capacity limited. So far, the limitation is not on the demand side, but the supply side.
Getting 100 million users in 3 months with 0 marketing or network effects already annihilates existing records, getting 10% conversion is nothing special.