We chose not to build an Apple Watch app prior to its launch precisely because it difficult to do good design and engineering for a device that you don't have and have never used:

http://blog.anylistapp.com/2015/04/why-anylist-is-not-availa...

See also:

http://www.macrumors.com/2015/04/29/qantas-customers-discove...

'Qantas's predicament serves as a sort of warning for developing an app for the Watch before actually having the device in hands to test. Qantas's lead app designer, Gabriel Santos, echoed a similar sentiment of difficulty in developing the app, describing the entire ordeal of building and creating the app without the Watch "a scary process."

"We initially locked in a concept but when trying it on the actual device, it didn't work as well as I thought it would," he said.'