I'm no marketing or product expert, but it seems like the best way to sell the Fighter's Pass would be to release the content in the Fighter's Pass, hah. I never really understood the release / announce schedule (or lack thereof) of the pass in the first place. Obviously the people that are going to buy it are going to buy it regardless, I personally was a pre-order first day everything Smash related, but the whole "Only buy this if you trust we'll make great content" that Sakurai has mentioned multiple times would be a much easier sell if they gave some indication of a schedule. Doesn't even have to be the character announced, just something like "Look forward to characters releasing in Spring 2020, Fall 2020, Winter 2020, Spring 2021, Summer 2021, and Fall 2021!" or something. And if they need to postpone or delay it, just push the dates or something.
The whole approach to Season Passes with defined numbers of content always seemed a bit strange to me.