The business value of missing a notification or meeting can be really high. I feel like businesses would happily pay $10 per user-month to have all their employees on time to a meeting. Or even just closer. I imagine similar logic can be applied to other notifications.
Maybe I'm being extremely naive, but isn't it already a solved problem with synchronized & shared calendars and notifications?
I think the idea is that the upcoming calendar/appointment notification is live and always on the menubar. See example screenshot from their web landing page: https://superpowered.me/static/media/menubar.aaa56b48.png
I'm building a similar calendar notification tool for personal use on Windows so I understand the value of this. Calendar notifications via email and "reminders" on the iPhone are not effective for my workflow and I need something that's always active on my menu bar.
I spend my time in fullscreen apps. The menubar is never visible.
If this is all you need, why not just use an open source alternative? I'm using MeetingBar (https://github.com/leits/MeetingBar) and it covers all of these "issues". It even sends notifications, it's lightweight, scriptable and doesn't cost me as much as a Photoshop subscription.