Sure, but taking a trip to White March, while you are going mad doesn't feel very sensible.
There actually is a reason to go there tied to the main plot: the Steward mentions having heard disturbing reports of the Leaden Key's movements in the area, suggesting that they have an interest in the ruins as they have in others throughout the game. In that sense, the Watcher's trip to Stalwart isn't much different from their trip to Dyrford, with both being little more than transit points en route to the far more interesting ruins that are nearby, even if the lead you get to head over to Clîaban Rilag is significantly more compelling given its source and Lady Webb's interest. The main problem that I see is that the Leaden Key angle potentially ceases to work as a motivator once you learn that their known agents in the area are already dead, though you could argue that the Watcher might remain interested in investigating the ruins that drew them there.
Sure, that is all true. I guess, I didn't really express my mind well as it is not the lack of explanation that bothers me. I think it is just how separate the expansion feels from the base game. New map, kinda different design (more packed and focused).
I feel like it should be more closely tied to the game, if it is going to be a parallel expension. Heart of Stone for Witcher 3 works well, as it starts as a regular quests, happens on the same world map as main game, and many of the quests will take you back to Novigrad. You can do expansion and base game at the same time. And story wise there is no conflict there. Blood&Wine on the other hand, I will always do after the main game is completed. It is a much more separate adventure and abandonig the main quest would be odd, even if the invitation Geralt gets doesn't leave much space for turning down.
To conclude: I won't mind a pararell expansion for Deadfire, if it is I more intertwined with the base game. However, if it is a more standalone adventure, I would prefer for it to be its own thing.