There is already a minimal amount of thermal diffusion modelling happening, but it’s an extremely expensive thing to maintain, so we don’t anticipate making it significantly more in-depth.
Yes
Your outline isn’t detailed enough to answer the question. You need to be more specific about what you’re trying to accomplish.
After a quick glance through some SS13 wikis, I’m very sceptical of this assertion. SS13 looks like it’s very much optimized for modelling a closed system, and making things intentionally complex in order to increase !!FUN!! Those are both probably perfect for SS13, but terrible for DDA.
It looks like a SS13 map is in the vicinity of 500x500 tiles, the DDA reality bubble is about 121x121x21 tiles.
This might look like it means it would be easier to track gas composition and pressures in DDA, but the reality bubble does not represent the entirety of the game. A given enclosed area can have a completely arbitrary volume, meaning there’s no way to bound how much computation you have to do to keep an atmospheric simulation consistent.
As for the complexity, unlike in SS13 these atmospheric effects would be the exception rather than the rule, which limits the value of making this system more complex.