If you add Kobo support and ship the Android app, you've got a premium member for life in me!
Currently, I use KoboCloud to sync cloud drive (Box, Google Drive, et al.) folders to my readers, one folder for each family member. I use browser extensions to create epubs for websites on the fly and save them to the cloud drives, but can't find a great-looking solution for mobile (Android in particular). Many sites I visit like HN comment sections just don't reformat well and it looks like you have a wonderful solution implemented for that aspect.
there's send by mail" functionality in Kobos via Pocket, but it would need you to spoof the sender for attribution ( https://help.getpocket.com/article/1020-saving-to-pocket-via... ) and the account to whitelist the email address prior. My impression towards "pocketed" hn-links is they're crawled once and not refreshed - so you miss out on many comments if the article was already cached when it had only a few comments.
I plan to add integration with dropbox and g.drive to my (similar) tool - Sendtoreader during September. Once that's done, reMarkble will get everything needed to receive web content, including RSS feeds subscriptions (full-text format)
That would be great. I've had formatting issues with Web-to-epub browser extensions so have been usin "Print Friendly" for web-to-pdf on desktop, and Shortcuts print-to-pdf on iOS.