The ITIN is likely the reason that you did not yet receive an economic impact payment as returns with an ITIN were not eligible for payment, even when the other spouse had a valid social security payment.
The IRS is not likely to issue a payment at this point for a return filed in 2019, even with an extension. However, this does not mean you cannot still receive the payment at a later date.
As long as your spouse has a social security number when you file your 2020 return in 2021, you will be eligible to claim the credit as a refundable credit on when you file your tax return.
Since there is some potential for additional payments to be sent at a later date, it may still benefit you to file an extension and wait to file your 2019 tax return when you have the social security number in-hand.
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