I don’t think this is quite operationalizing “this question will be legally tested and it will be found constitutional to ban it”.

For one, it’s not necessarily the case that a plea bargain precludes a constitutional challenge to a law. You could retain the right to challenge in the plea agreement. I think you have to explicitly give the right up to be unable to challenge the law.

It is reasonably possible perhaps likely that if the Supreme Court does revisit the issue it will be in this situation.

Alternatively what if this issue is litigated pre-trial, with an appeallate decision saying the law is constitutional, then, on losing the constitutional appeal, the defendant pleads?

If the conviction is overturned on appeal, it doesn't count. If all such convictions have pending appeals as of closing, I will wait for the appeals to finish.

Related:

This is a different way of operationalizing Isaac's market. That one is about de jure legality, which might remain open to interpretation. Mine is easier to resolve.