Terraria 1.3: Xbox One Submission Approved! Launches Monday, February 5th!

For the Xbox will mod ever be added or is that not possible?

 

Short answer:
It's not possible.

Long answer:
Current Terraria mods (tModLoader tAPI) do their stuff by directly changing the game's code. This is not allowed on console as that would open up the possibility of hacking the system. The console makers (Microsoft, Sony) won't EVER allow this.

Modding in games such as Fallout 4 work differently, mods can only change things indirectly through scripts that have limited functionality. Mods are limited in what they can do.

Adding a similar support for mods in Terraria would require rewriting the game from the ground up. That is simply too much for an indie developer such as Re-Logic. They don't have hundreds of people like Bethesda have.