what is the highest TAM crypto startup possible to build today?

best answer wins a cofounder

+1 as the hardest / most needed thing to build

what is the tam tho

do you have some favorite resources / past experiments on this?

I think of it as a new global money. Anyone can use it to store value, or to trade value (buy things). So in theory it has the tam of a global currency (the whole economy).  

Question is how do you monetize (and of course the obvious question of how you actually build/scale it!)