Honestly, I'm kinda for 6 classes. There is absolutely 0 reason as to why the WPIAL cannot combine classes in some way and determine its state rep by some other means. The WPIAL can have 4 classes if it wants.
Combine 5A and 6A
Combine 3A and 4A
Have a regular 16 team playoff. If a 6A beats a 5A team at Heinz, both advance. If 2 6A teams beat 2 5A teams in the semis, the 5A teams play a defacto 5A championship for the state bid. If there are 3 6A teams in the semis and 1 5A team, the 5A team gets the state bid. If there are 4 6A teams in the semis and they all beat 5A teams in the quarters, you can have a defacto 4 team 5A tournament the next 2 weeks.