A note on the invite graphic...
They're rounded corner squares, simulating a type of halftone pattern to create the shading by shrinking the tiles, which could mean:
1. Icons from iOS, perhaps hinting OS X may take a similar route?
2. Pixels with more detail, aka retina / high density / 4K displays
3. TVs
4. Multiple screen sizes (Phones)
5. Vector assets in the OS for fully scalable UI elements.
Among others..