From what we know about Infusion, it's a new campaign, taking place in a separate part of the Underrail.
As we know from the end of the original, Tanner fled to North Underrail, with Six and the player pursuing him in some of the ending slides. Also, while the fate of the ACoNR is unknown, it's fairly plausible that it would've either ended up with the player/Six, Tanner, or Aran, who would've returned to Hexagon after completing his mission.
Given all of this, it seems likely that Infusion will take place in Hexagon, and maybe even parts of Dis, the largest known city in the Underrail.
This hypothesis is also supported by some of the screenshots in the Devlogs, with the interiors shown looking electrical in nature, as well as being rather cramped, reminiscent of the descriptions of Hexagon given by Oldfield and Seeger.
Honestly, though, where else would the sequel take place? There are way too many hints for it to be anything else, even excluding Expedition.
The real question is, who is the third Godman, and why is it actually Hank Wardell?
