Agreed. Reserves are reserves. Any asset class that's viable will be held in reserve as collateral.
Discussion
And they can’t manipulate it since it’s not proof of stack
Well it may be similar to the microstrategy Struct, where Coinbase holds the actual reserves on behalf of the custodian.
Similar to how London vaults are meant to hold the gold.
Where the issue comes into question, who else is declaring their stack off the same wallet address?