didn't know about the old Stillwater spur so decided to look into it and made a quick drawing of it
Green is the main line that the Eau Claire train would use, orange is the ROW that still has some track, and yellow is the ROW that doesn't (pretty sure its a bike trail now)
In summery the spur is about 6 miles long (4.5 with track, 1,5 without) so I see two possibilities
If demand ever grows for more trains, west central wisconsin rail coalition (group behind the project) can divert some trains to Stillwater from Hudson (possible but would take years of the train successfully running)
Stillwater and the other cities along the spur can invest into making it a new lrt/streetcar inturburban/etc. that connects to one of the stations (to bad that's definitely not gonna happen)