The performance of Metal is impressive.
About 1 or 2 years ago, when CoronaSDK upgraded to a new version of OpenGL, I found my app’s performance had a big jump (much more smooth). I didn’t know it could make so much difference when Corona made some fundamental changes.
Corona should support Metal proactively. That will be another big jump in performance. Good for the developers, and good for Corona.
Crossing platform will be less and less important (many alternatives or going native). It’s the whole package that developers choose Corona. If Corona cannot catch up with the speed of Apple’s development, it will be left behind, especially for such an important feature.