An 18-member team is at work on an ambitious mod introducing a completely new region to the Fallout world through Fallout 4, though it is "several years away" from completion.
Fallout Cascadia, set in post-apocalyptic Seattle, aspires to offer a map roughly the size of Fallout 3, but with more quests and locations than the Far Harbor DLC just launched. The modders will release it for free.
Work on Fallout Cascadia began six months ago, but with the Creation Kit currently in open beta on PC, work has intensified and the team wants to get word out.
However, the team says "the expected release is several years away." That's far enough out that there is no way to tell if it will work on consoles. The team does plan to share the mod through Bethesda.net, which would make it available to consoles.
Fallout Cascadia is meant to take place several decades after the Fallout 3, Fallout: New Vegas and Fallout 4 timeline. Modders plan to include familiar Seattle locations as well as others around the city, including Mercer Island, Redmond and Bellvue.
The mod team has set up a subreddit and social media feeds for others to follow as development progresses. Information for volunteering for the mod team is at the link, but they're not looking for voice actors right now.