If someone went to court in support of the right to own slaves, would you consider that to be a viable challenge even though the Constitution is quite clear on that issue? Or is it settled law that it is against the law to own slaves?
Of course it’s a viable challenge! The nature of the Constitution is that it can be amended and those amendments can be challenged in the courts for Constitutionality. There is no such thing as settled law. Otherwise, lawyers would not have a job!