I believe it was open at least once last year (or the year before) early in the season. I didn't really look later in the season as I was too big to ride. That is the last time I personally saw it open.
I feel like they are less of the park's worry now. Seeing Verbolten was built without a single rider line (they will not let single riders through the QQ line). But also interesting to note that Loch Ness doesn't have one either (not sure if it ever did).
Main reasons why the single riders lines aren't used is they cut down capacity by a ton. You have to laud a train AND then you fill in empty seats. Usually adds up to an additional 2 minutes to a load time. It's just quicker to cycle to the next train.
Interesting. I think to implement a single riders' line, you'd have to have the seating for the next train sorted out ahead of time (like you see at Disney and some rides at Universal). That would take at least one extra employee and a redesign of some of the stations at BGW.