I don’t play Hearts of Iron IV myself but the premise seems interesting and I wanted to share it.
This is the map and I feel like they did a decent job making it feel like a Fallout map even if they had to extrapolate a lot of the lore and use some non-canon material like Fallout Brotherhood of Steel for the Texan Brotherhood for example.
That said I don’t know if some canon groups, that could have been added, are present like the Oregon cannibals from Fallout 2 and I feel like they could have used locations from the cancelled Fallout Extreme to fill out the NW corner of the map.
It’s a pretty cool mod! I still remember when I first played it, the map pretty much only had the NCR, Legion and areas in Utah and Washington. It has come a long way since, and afaik they plan on populating the whole map with all kinds of factions. The next update will clean up some of the north-east areas of the map.