I, too, join the cohort of surprised observers from this week's argument. For me, the biggest takeaway is not so much that the Justices were engaging in textual sport, it's that they wanted to engage in those gymnastics. That is, everyone seemed to get how unjustifiable the legal status quo is: it's clear the law is dumb, it's probable that Congress made a mistake, and so the Court had a very roll-up-their-sleeves attitude that struck me as, "What can we do to mitigate matters while being able to sleep at night that we are following an at-least-plausible reading of the text?" The subtext to that is that they were not searching for the most natural reading of the text but the reading that did the least harm that could fix a problem. (Surely a different colloquy would have ensued had the Late Justice Scalia been present!)
Note this is not "judicial activism" in my mind, because if it were true activism, they would just make up a doctrinal canon saying they can ignore the text when "manifestly unsound," or maybe open up the absurdity doctrine so wide you could drive a Jones Act tanker through it. I see this as remarkably pragmatic. We have to follow the text. If you can get us a reading that we can live with, we'll do it. That's why they kept pressing on what is the justification for this law. Their lack of enthusiasm to any proffered makeweight (treat triple tax-exempt bonds differently from PR vs USVI?!) was telling. If you're a judge, especially a Justice, I suspect you don't feel bad interpreting a law in a creative way if everyone but the self-serving litigants seems to suggest it's pointless. In fact, you probably feel good.
All this said, don't get too excited for reversal yet. The bondholders had some good textual counters in their briefs that didn't make oral argument. But the irritation of the engaging Justices with the law, coupled with the simmering undercurrent of subjugation inherent in the territory's second-class status, suggests this really could be an interesting opinion.