For me it is not a book that teaches Racket though - and not a book to pick up web dev in Racket though.
If there was tutorials on how to do Sinatra, Express or Flask style web apps/apis I think people who use those types of frameworks would find it more accessible. And there are a lot of those type of people.
Specifically:
Well designed and communicated homepage.
Modern products and companies using the language. Their websites should look great too.
Boilerplate-free graphical or web app oriented examples.
If a clean, well designed language with good documentation and bite-sized clear intro videos could do this today, it can build momentum.
Ps: I'm a designer who would love to get into programming with Racket.