Most notably, right now the limiting factor on Apple Watch isn’t really component availability. First things first, Apple needs to finish the development of the Apple Watch software and hardware internally.
To date, all of the Apple Watch’s handled by press have been non-functional, showing only non-interactive videos of the user interface. This means that Apple still has a long way to go before the device is in any kind of shippable state. It has been previously rumored that Apple is working hard to improve battery longevity, for example.
Moreover, although Apple has announced WatchKit, which will enable third-party developers to create interactive notifications for the Watch, no SDK has been released to actually allow development. Apple Watch integration may come as part of iOS 8.2 for example, which is currently in development.