Ah, but the provision of the original United States Constitution that forbade congressional action against the slave trade also had an expiration date (1808). That provision, however, is distinguishable from Pakistan's 21st Amendment on three grounds. First, it was part of the original grand bargain by which the sovereign states agreed to subject themselves to the new Constitution; second, rather than granting the new government a power for a defined period, it withheld one; and third, it had a 20-year term -- a far cry from the mere two-year duration of a single Congress.
Admittedly, if this masquerade-amendment argument were embraced by the court, it would leave the door open to Parliament simply to enact the same measure all over again, but this time without an expiration date. There being no evidence that the politics of military courts with jurisdiction over civilians have materially changed, that could well happen even if Parliament next time around were to conduct a serious debate rather than permit itself to be stampeded into precipitous action. The court would have merely kicked the basic structure can down the road, and would need to confront it once again, this time without an easy out.
Still, might the more limited, less invasive rationale proposed here be a graceful and broadly acceptable way out of Pakistan's current constitutional dilemma? Comments invited. (Real names only, please.)