Who's to say they won't?
Again, we currently have 4 unused characters in World of Light.
This pass is the exact same price as the prior one, despite having 6 characters, but I can't see a future where Nintendo both:
A: Puts out a pass with 4 characters
B: Keeps it the same price as the last 2 despite having less content
Right now, these 4 unknown spots are an anomaly. We don't know if they'll be Echo fighters or what, and the fact of the matter is, we're going to have more General Directs than FP2 characters over the next 2 years, that's just obvious.