1. It will be a lot better if the Summary popup can be stretched to full-screen with font size controls.
2. There needs to be a feature to browse papers based on subjects and other applicable categories.
3. There need to be playback controls (pause, rewind, etc.) for audio narration of the summaries.
4. Themes customization and dark mode will also be great features to have.
Really love the concept by the way!
But you're probably better off discussing monetization with the other more intelligent experts here. I'm just a lurker :)
The content processing could be good, especially if it was to decrease the complexity of the language and simplify the concepts. I would take care that the descriptions could be horribly wrong and misleading.
I would probably look to monetize in a different way:
1. Synchronization of papers across devices.
2. Notes on papers, that could also be shared.
3. A service to find publications of that paper (arXiv isn't always updated with this).