I'm learning Angular nowadays and this project seemed to be a perfect one for a rewrite. I planned to do that beforehands mainly because of the design and slowliness (frontend issues) anyways.
I kept PW as the API source, so I could use the current admin as before. The major change was to remove all template files except for "admin", and added a new "api" template. Of course a bunch of frontend modules were also removed, eg. TemplateLatteReplace.
Things are determined in ready.php.
There's also a saveMeta() function that creates a meta.json file on the server, that is to be able to dynamically update the Open Graph meta (and page title) in the Angular entry point "index.php" (renamed from "index.php"). See more about this here.
There was some unforeseen issues during the development but mostly on the Angular/.htaccess side. ProcessWire itself was easy to handle, my biggest concern was to design the JSON response in an easy-to-process way.
Although the initial load may take slightly more time, the speed and responsibility is almost instant afterwards. Images and video thumbs need additional requests but otherwise everything is very snappy. You can read some more about the site on my blog.