Very true. The last three nationals it felt like the top ladies took nationals for granted and decided to so well enough to go to worlds. If there were two slots maybe it would train the ladies to be on their game for next year.
I feel like Ashley is going unnamed here

. Honestly, at her age, if she wants to hold back at Nationals and save her best for Worlds, I have no problem with it.
Ultimately, whatever happens on the GP matters more than at Nationals, when it comes to Worlds spots/performances. For US ladies, making it to the GP final = a trip to Worlds. Do international judges pay more attention to the GP series or to US Nationals? The GP series matters more; that's where you're building your rep. Generally speaking, a GP medal means a trip to Worlds (aside from Mirai in 2014, who won a bronze on the GP series, but had a worse season than Gracie, Ashley, and got beat by unknown Polina at Nationals).
Mariah won silver at SkAM this year and ended up on the Worlds team. Gracie skated awfully on the GP all season and is not on the Worlds team. If Ashley had bombed all season on the GP, maybe she wouldn't be on the team, either. But she won a gold medal, which is more than any other US lady did.
Karen and Mirai have had plenty of chances to prove themselves on the GP, and they haven't, so Nationals really, really mattered.
This is true elsewhere, too. Russia isn't just sending the top ladies at Nationals - they're the top Russians at the GPF, too.
In the interest of making predictions wayyyyyyy too far ahead of time (so I can point to this post later and say that I was right), I think next season will be Mariah, Ashley, and Gracie battling it out, partially because I think they're most likely to be successful on the GP series, as compared to Mirai and Karen.