So, as far as I know, methane breathers were in vb6. So I guess they will also appear in C#, especially that the system generation already likes to spawn a "methane equivalent" of an npr-habitable world.
However, why limit this to only oxygen and methane, on top of that having a narrow range of temperature? I think it'd be cool to open up the possibility for life generation. Just think of the possibilities: Venusians, a race thriving in extreme cold on hydrogen-based superearths, a toxic world full of chlorine and sulphur dioxide hosting some sort of exotic life for which oxygen is the equivalent of mustard gas, maybe on some rare occasions some species that don't adapt well to any atmosphere and thrive on airless planets, nitrogen breathers, basically all kind of unique and cool stuff. Of course finding life on airless rock shouldn't be as common as finidng it on earthlike planet, so this would require tinkering with probabilities of each "type of life" to spawn, but in general would make the universe much more original and unique.
