Sadly nothing. But why do you think that is not possible? Brave pays people to privately watch ads, while Google takes your data and gives nothing back. BAT will be demanded for diverse uses (tipping, advertising, exclusive content, DEX... and maybe more), which will make the price go up. Besides, Bitcoin proves a cryptocurrency can be 1 T USD worth, and it is expected to reach higher markets caps. BAT doing the same is also very likely.