Given how early we still are we first want to focus on podcasts and make sure we nail the functionality & experience. In the future, we then want to enable users to also upload their own audio content (e.g. an audio book) and benefit from all of the same features.

For now, we haven't really thought about enabling text mediums and going the other way around (text to speech instead of speech to text). You could however check out the Matter app. Not sure whether you can upload your own pdfs, but you can do text-to-speech for blog posts, including highlighting. They also have a Readwise integration like us.