Jefferson Lines just posted on Facebook that they're starting service from Sioux Falls to Winnipeg (with numerous intermediate stops and connections) starting August 16.
While the timetable (shown below) isn't great for connections to/from the Empire Builder, the connection is at least finally there in some fashion, and southbound from Winnipeg it appears that the connection to the westbound Builder is solid. Eastbound doesn't work, unfortunately, though Jefferson Lines will be happy to take you eastbound to many of the same destinations on their own fleet.
I can imagine it being very popular on weekends for Winnipegers to go down to Minneapolis/St. Paul (connection in Fargo) and shop for a weekend. I'll likely use it at some point from MSP just to say I did - the pricing (probably promotional for now) is very reasonable at around $25 one-way from Minneapolis.