Focusing on your own day-to-day problems ends up with the various VC-funded "mom apps" to summon contractors who to come to your house, pick up your room, and do your laundry for you, make that statement old advice and not to be taken literally.

I agree that more complex reminders with the features you describe would be quite cool, for both code reviews and birthdays would be cool, but you admit that the business case isn't quite there yet. (There is a glut of reminder apps on the app store, those features probably exist between all of them.)

Better sync software falls under the category of development tools; even Visual Studio is free these days (in the form of VS Code) because selling to developers is notoriously difficult to sell software to, because they know how to code. (There is also no shortage of open source inotify+rsync based sync tools.)