It wouldn't, according to accounting principles. It would be accounted for as deposits received, with a balancing liability for when the customer makes a purchase or withdrawal.

They would only record revenue when they charge a transaction fee, or any other charge/income that can't be used by/returned to the customer at their discretion. Revenue is only revenue if it doesn't incur a matching liability.

I agree that that's how it should work, but I wouldn't be surprised if Coinbase wasn't completely orthodox in their accounting. Replies below indicate that they may indeed be counting customer deposits as "revenue".

They have like 20m users, that would mean $50 deposited per users so.. no

Per sources connected to their Finance Dept, that $1 billion in revenue does include amounts that would not normally be included in revenue under generally accepted accounting principles (GAAP).

Coinbase and GDAX products operate differently.

Coinbase is a counter-party in all trades e.g., people buy FROM Coinbase or sell TO Coinbase. So $1B revenue number would include all deposits.

GDAX accounting would only count commissions as revenue.

Also, how much of it is in fees collected and stored as cryptos themselves? If crypto takes a dive, does their revenue retroactively lose value?

That would be asset, not revenue.

You mean Asset Under Management or AUM?