There's no legal basis to treat a tax that is not collected as income. The IRS would never consider it income, and only an incredibly incompetent Congress could turn it into income, and if that happened I'm sure the courts would rule against it quickly.
The risk is that you will still have to pay your full social security tax. If you spend the deferred amount, you might be on the hook for repayment later, unless Congress (before or after the election) passes a law to forgive the uncollected tax.
But there is no realistic concern in my humble opinion that an uncollected tax would be treated as taxable income, even if the tax was canceled by a new law instead of just being deferred.
