At WWDC this year Apple continued their trend of offering more app frameworks & integrations points. Apple now offers the full App Store experience for Mac, iPhone, iPad, Apple Watch, Apple TV, Apple Maps, Apple Messages & Safari Extension Apps. And then I'm skipping custom keyboards, ad blockers, today widgets. Those were last year's news.
What does this mean for developers & product designers? More separate app experiences to create, test & distribute. More complexity. More app targets in your Xcode workspace. More things that can go wrong. App development just got a whole lot more expensive.
It's no longer enough to "just" build an iOS app. You need a Watch extension, rich notification support, a today extension, etc ... There's only ONE way to deal with this complexity: iterative development.
Start with the core of your app in iOS. Release that to (Testflight) user. See how users respond to it & only THEN build out the extensions like Apple Watch etc ... Setting out to build everything at once is the best way to make sure you will never release your project. Babysteps.