The reason I say this is simple. There is largely no retention for games on consoles. Games have a short life cycle and become stale in a matter of months. Before you know it, there's always a new major release or something else around the corner. Especially with major annual franchises such as Call of Duty and Assassin's Creed, people just don't have time to play the same game for years and years. It's the main reason MMORPGs have largely not been successful on consoles.
This leads to my next major point. Some of the best mods are years in the making. We aren't going to see much in the way of anything great in terms of mods for a while (especially without the Creation Kit released). The reason modding works on PC is because PC gamers will literally play BGS games years after they have been released. There is still a dedicated modding community for Morrowind, and it released 13 years ago. How many console gamers are still playing Morrowind on the original Xbox?
The other issue is console gamers won't be getting mods immediately like PC, especially those who purchase the game on the PS4. By the time mods start making their way through the channels, more than likely much of the player base will have beaten the game and moved on to something else. The only hope BGS has is their season pass will incentivize more longevity and that others will come back for the new DLC they release, exposing them to the mods that have been released.
BGS really has a small window to hope that mods catch fire. By the time the modding community has even developed enough to provide anything substantial for many, I think most console gamers would have either traded Fallout 4 in or it will be collecting dust on a shelf somewhere. I think mods will provide more incentive to play BGS games on consoles, but I don't believe they'll have the same kind of impact on sales that they do on PC for a multitude of reasons.
I haven't even mentioned the fact that BGS will censor what kinds of mods are even possible on console. Some of the most popular mods use third party software (script extenders, mod manager, enhanced natural beauty, sweetFX) which won't be possible or legal on consoles. Other popular mods, such as advlt mods (excessive gore, nudity, etc.) won't be allowed either due to ESRB restrictions. There also won't be any mods that improve textures, graphical fidelity, distance draw, number of npcs rendered, etc. due to the locked hardware. This will leave what few mods consoles have largely being cosmetic and probably not that compelling for many.
I think it's great for all parties concerned that mods are coming to consoles. I just don't know if they will really work as the platforms are too constrained to really take advantage of what makes modding great and console gamers won't have the patience to wait.