For me, the issue is that TSA rarely, if ever, reduces its screening footprint.

So let's assume for the sake of argument that there's actionable intelligence that says that insulated liquid containers merit additional screening. Is this a temporary procedure or a permanent one?

I fear that it's permanent. Thermoses get added to the eternally growing list of "exploitable devices": laptops, shoes, bulky clothing, liquids, CPAPs, printer cartridges, and so on.

And then, six months from now, when someone figures out a new transportation mechanism, we'll add another item to the list, and so on. The inevitable outcome is a situation in which all carry-on items are banned --- and, of course, the airlines very carefully disclaim all liability for lost or stolen items from checked luggage.

I can only think of one situation in the last ten years in which a banned item was later un-banned: cigarette lighters. Are there others?