Vinson did state that an injunction wasn’t necessary,
as the law was now void,
and he had the expectation that the Executive would comply with the law.
Now, who’s gonna enforce this compliance?
Therein lies the problem. Vinson expects that the Obama administration would comply with the law. But, without the injunction, there's no way to enforce compliance.
So, they are free to ignore him, with no consequences. Maybe he'll impose an injunction, then. But, given the rules of jurisdiction, the administration can simply avoid doing anything in the northern district of Florida, and there won't be a plaintiff that can show injury by non-compliance.