tmp variable is not particularly special actually, it's used for different things depending on the situation.
But yeah I kinda agree. :O Just the biggest issue is that because it's so old, it's very likely that screwing with it, even to add massive improvements, would mess up a lot of older saves that may have relied on the lack of those very mechanics.
It might get changed someday, who knows.
I kinda like the idea of "growing rings". But it's triggered by tmp. So it maybe useful.
And plants.