Update: UIKit works!! More complete post & info incoming, after http://hackthenorth.com/ (where I am now) is over.
Attempting to get React Native to work on watchOS 2, starting with trying to get just UIKit working like @steventroughtonsmith: http://blog.steventroughtonsmith.com/post/128957959685/native-uikit-apps-on-apple-watch
The 'ActualWatchApp' framework target is linked to React Native headers via Cocoapods; currently just trying to get the 'PlainWatchApp' framework target (which isn't linked to React Native) working.