Given B is often very quiet, I have my doubts they’d invest in a lounge at C. What seems more likely would be to take one of the A lounges offline for renovations and then direct passengers departing from B to the B lounge well in advance of their flights.

As it stands, gate assignments aren’t communicated to many passengers until they’re already in the lounge - passing this info on earlier and proactively directing passengers to other spaces would help a lot.