Actually I agree with the initial article's author's premise that any other civ would most probabalisticly be much older and much more advanced, but your rejoinder nails the problem. How can we possibly surmise what such a putative super advanced civ would do or could do sufficiently to form a new paradigm detection strategy? Remember, we're not talking about intercepting 'signals' intended for neophyte cive but detecting byproducts of their technological existance. Even so, I agree it's worth making some educated hypothethes, floating them around for discussion via published papers and seeing what concrete scientific approaches result.

Me, I cannot forecast with any confidence the technology that WE might have in 2050 and its implications never mind that of an alien civ 1 billion years more advanced.