To me, the real problem is the Supreme Court must already have a decision made. If they decide in favor of subsidizing in stark contrast to written law the Supreme Court will be dead. The only possible arguments are political.
I think that the Supreme court taking this is a very good indication that they will rule against subsidies for the Federal exchanges. All lower courts have ruled FOR subsidies for Federal exchanges. There is no reason for them to take it if there aren’t differing rulings in lower courts unless they feel those lower courts are wrong.
Of course IANAL (constitutional or otherwise).