Decided to revive SubNot, I think I got an idea on how to make it work. The developers provide the Keys, and the bots, instead of SubNot being responsible for that. SubNot will still be the sender of the notifications, and could be potentially IP blocked from services if abuse is detected, but I don't know if it will. I will continue developing it anyway, because it is something I like.
Today I implemented a basic version of the browser notification, the users are able to register to get browser notifications. From what I tested, works at least on Chrome, Firefox, and Chrome for Android, so it gets a lot of users.
Need to polish it more tomorrow, and then add filters to the notification subscriptions. It entails creating temporary tokens that will be redeemed once the Telegram subscription is done, because the amount of information that can be passed to the start parameter is very low.