Did WISE detect Dyson Spheres/Structures around Gaia-2MASS-selected stars?

Soon after the release of the WISE all-sky catalogue of 500 million mid-infrared (IR) objects, suggestions were made that it could be used to search for extrasolar devices constructed by an advanced civilization to convert a significant fraction of their host star's luminosity into useful work: "technostructures", "megastructures" or "Dyson spheres/structures", hereafter DSMs, whose inevitable waste heat would be seen by WISE at mid-IR wavelengths. However, a trawl of several million potentially-habitable Gaia-detected stars for mid-IR-excess signatures is fraught with danger, due to both noise from such a large sample and, more importantly, confusion with the emission from dusty background galaxies. In light of a recent claim of seven potential DSMs in MNRAS, a brief rebuttal appeared on arXiv. Further to this response, the relevance of WISE-detected galaxies is discussed in more detail, leading to a seemingly tight limit on the number and lifetime of DSMs, and indeed intelligent worlds, in the ~600-pc-radius region patrolled by Gaia. However, the detectability of DSMs is questioned: a DSM might extinguish its star at optical/near-IR wavelengths, and thus either not appear or appear anomalously faint in a stellar catalogue. Moreover, a civilization advanced enough to construct a DSM is likely to be advanced enough to use countermeasures to mask its presence from us.