Tau has been rejected already by the Luau team; it’s constant folded anyway, so it’s no big loss outside of your readability.
Otherwise, you can always open RFCs for math functions like math.alpha. You can read more about that process here.
For reference this is the RFC that Zeuxcg wrote for math.lerp: math.lerp | Luau RFCs.
Though they generally don’t have to be that advanced, depending upon the feature you’re proposing. Here’s one I myself wrote for bit32.byteswap as an example: bit32.byteswap | Luau RFCs. Notice how its much simpler than the math.lerp one, because the function itself is simpler.