You are right that Scientific Speculation Codidact is primarily about extrapolation from currently known science. (It was conceived as a more focused, somewhat more science-y counterpart to Stack Exchange's Worldbuilding site.) It's possible to extrapolate yet provide some kind of evidence, such as giving a current scientific basis and reasoning leading up to a conclusion, for that extrapolation and the results of that. Example: as far as I know, we don't have any evidence of non-water-based life, and generally liquid water is considered a prerequisite for life as we know it, but we can still speculate about how such lifeforms may be able to use other compounds as solvents and provide, say, a chemistry-based reasoning for why a particular suggestion is more or less likely. So while a biology community might consider such a question off topic for being too speculative, it could have a home on Scientific Speculation.

Thanks for the explanation. That is more or less what I thought it would be. If current science doesn't know yet, one can speculate but one cannot simply break fundamental physical/chemical laws in order to make things works. Instead one should hint at how things could work.

Trilarion‭ Pretty much. It might even be reasonable to break currently known science (and engineering) if that can be justified; the hypothetical Alcubierre drive, for example, requires matter that has negative mass, which we have no idea how to make or even if it can exist, but it's still possible to postulate the existence of such matter and say "based on the assumption that such matter can exist, here's how a FTL drive might behave". (It's also possible, of course, that the Alcubierre drive is simply a situation in which Einstein's equations break down, similar to how singularities or relativistic speeds is an example of where Newtonian equations break down. As far as I know that hasn't been settled yet, but it's still possible to postulate and then speculate, if the postulate can be justified. IIRC the Alcubierre drive hypothesis started with a physicist pretty much saying "I wonder what happens if I plug negative mass into Einstein's equations...".)