If there were to be a way of modding on console Terraria, it would have to be part of the app itself - in the same way that FO4 or ESV:Skyrim do.
However, getting permission from Sony/Microsoft is very unlikely and any modding that they might allow would be very restricted. For example, both those games do not allow mods to add new assets (graphics, sound, models etc), only modify ones that already exist in them. So you could modify a 10mm pistol that already exists in the game to fire mininukes in FO4, but you couldn't make an entirely new weapon with new models and graphics.
Homebrew is strictly forbidden by Sony (and I assume Microsoft - never had a XBox so I'm not sure) and having a modified PS4 will likely result in getting hit with the Ban Hammer and your console being network banned. I'm pretty sure discussing console homebrewing isn't allowed on this forum so the less said the better.
In short - unless the developers reach a deal with MS/Sony it won't happen, and even if it does it wouldn't be the same as PC.