a legal sport betting site that 1) allows you to deposit and withdraw bitcoins

You are thinking in old terms. Future betting should happen onchain, LN and / or in other L2, using multisig, 

 and other smart contract techniques, no single site holding your bitcoins at any moment.

bitcoin

What will let you say: "Bitcoin is unstoppable and now belongs to the masses"? 

gatto

Bitcoin is already unstoppable.

> a legal sport betting site that 1) allows you to deposit and withdraw bitcoins

You are thinking in old terms. Future betting should happen onchain, LN and / or in other L2, using multisig, [DLCs](https://bitcoinops.org/en/topics/discreet-log-contracts/) and other smart contract techniques, no single site holding your bitcoins at any moment.