Tailwind isn't really equipped for incremental builds like this, but what I think is that you would have to run Tailwind every time you send through one of these JSON packets. Instead of using tailwind.config.js, you could run postcss with the Tailwind plugin and pass the Tailwind config inline. This gives you the chance to send the classes directly:

const postcss = require('postcss');
const tailwind = require('tailwindcss');

/**
 * Generates Tailwind CSS from given class names.
 *
 * @param {string} classNames Space-separated list of strings.
 * @return {LazyResult} The process result.
 */
module.exports = classNames => postcss([tailwind({ safelist: classNames.split(' ') })])
  .process('@tailwind base; @tailwind components; @tailwind utilities');

(Not sure if this code would actually run, but something like this! Taken from PostCSS JS API documentation)

You could also see if Tailwind has a JavaScript API and do something similar without the need for PostCSS as an intermediary.