You are indeed correct that GaAs has been used for quite some time.

The game changing aspect is POET (Planar Opto-Electrical Technology) using the critical VCSEL (Vertical Cavity Surface Emitting Laser) platform.

POET can be used on Si or GaAs but offers the following :

By enabling increased speed, density, reliability, power efficiency, and much lower bill-of-materials and assembly costs, POET provides a new technology direction and opportunity for the semiconductor industry.

POET will allow continued advances of semiconductor device performance and capabilities for many years, overcoming the current power and speed bottlenecks of silicon-based circuits, and will change the future development roadmaps of a broad range of semiconductor applications including mobile and wearable devices, computer servers, storage arrays, imaging equipment, and networking equipment.