Hi everyone,
some Mods or part of Mods are that awesome, that you may have thought “Why is this not part of the main game?”.
I had that thought a few times 
I do not even know if this is possible or if the devs/mod makers do/would want this to happen
BUT lets fantasize
Here are the conditions:
Only one mod or part(s) of one mod is allowed
You can choose the same mod as others
You have to explain why it should be in the game
Okay, I will start:
there are a lot of really really good mods BUT if I had to choose one, I would takes this:
This is not the mod I like most, sorry relyss 
but this was the first mod I did use and this is the only mod I am using in every single game I have played, since then.
There are some double colors or at least there are some colors which I am not able to tell apart.
But to be able to use more colors and even terrain colors is a greate benefit and I am using it pretty frequently
And what is your MOD which should be in the main/vanilla game?