Taking the account as collateral is only viable if you're able to secure it. That is, any value on the account should be multiplied by the probability of the original holder not running away with the account with a reset.
This is why in my eyes, accounts should be taken as collateral only when you're willing to give the same amount to the user as if they were requesting a zero-collateral loan.
Else If the Lender is cunning enough then, he can ask the user to provide the original email address and after changing the email, the lender will delete the email of "Reset the account within 14 days" from the original email and return the original email to the user.
In this way the lender can easily secure the account IMO.
Moreover i too think accounts should not be kept ad collateral.