At today's E3 2018 conference Bethesda confirmed a lot of facts about Fallout 76, but not whether it would have mod support or not. Considering one of the points of apprehension fans have had with Fallout 76 so far, not mentioning mod support is not a good look for Bethesda. Mods are arguably a huge reason for previous Fallout and Elder Scrolls title's longevity in the public conscious, so the big question that remains about Fallout 76 is, "How will mods work?"
Fallout 76 Mod Support: Will it Only Support the Creation Club?
Fallout 76 sounds like it will be always online. Unlike previous entries, which were all single-player, this game will depend at least partially on a connection to dedicated servers to play. How much it will rely on an online connection during solo play hasn't been discussed yet, but if the multiplayer drop-in/drop-out we can be pretty sure that it'll be always online.
This could be a disastrous move for mod makers. Fallout 76 looks like it'll offer plenty of opportunity for PVP and that means that there will be some sort of anti-cheat measures in place. Part of those measures will likely be a file integrity check, which means that if you modify the game files, you either won't be able to play or worse, you'll be banned.
More than likely, if mods are available for Fallout 76, we'll have to download them from Bethesda's Creation Club storefront. That seems to be the only logical way that mods could be vetted and applied to the game in a way that won't flag anti-cheat protection.
What this means is that each mod will be more like micro-DLC than the open house that you can find on Nexus Mods or Steam Workshop. Unfortunately, it seems like gaining multiplayer capabilities for Fallout may have cost us the extensive amount of mods we've seen in previous games.
Of course, I could be wrong. Bethesda hasn't yet commented on Fallout 76 mods. However, it doesn't look good so far.