The use of commas to separate key-value pairs here is perplexing to say the least, why have them at all? Does it means I now need to escape them if my value has a comma at the end?

From the docs:

  restish POST api.rest.sh \
    platform.name: HTTPie, \
    platform.about.mission: Make  APIs simple and intuitive, \
    platform.about.homepage: httpie.io, \
    platform.about.stars: 54000, \
    platform.apps: [Terminal, Desktop, Web, Mobile]

I appreciate that they have the following page which helps answer the very first question i had upon reading the intro, namely how this compares to a couple of existing tools (like curl, etc.): https://rest.sh/#/comparison

The site seems down (just blank white page).

cool to see the CLI community building stuff