Do we have a "longevity" estimate for Tabby's star?
By estimating how much starlifting would explain the observed luminosity drop, and then backing out the expected increase in the star's life against its flux decrease one could estimate how efficient the "aliens'" energy-harvesting technology is (coupled to a financial discount rate).
Plug its estimated mass (1.43 solar masses [1]) into the expression for main sequence lifetime [2] and you get ~4.1 billion years. But we don't know how old it is (the prevailing assumption seems to be it's old enough to have settled into staid middle-age behavior, making its variability harder to explain [3]).
By estimating how much starlifting would explain the observed luminosity drop, and then backing out the expected increase in the star's life against its flux decrease one could estimate how efficient the "aliens'" energy-harvesting technology is (coupled to a financial discount rate).