Hi Dave! I didn't realize the PlayCanvas engine was standalone like Three.js, I somehow assumed it was linked with the online editing tools you built. Good news! Really impressed with your physically-based shading support by the way.

We went with Three.js because it's pretty versatile and does everything we need in the near future. Superpowers is built in 3 layers: the core (which handles projects, storage and networking), the system (which is basically Three.js + game instance/actors/components) and all the editor & asset plugins built upon the system. The system can be swapped out with something else, and a new set of plugins can be built on top of it, or the existing plugins adapted for a new engine, so the community will totally be able experiment with other engines including PlayCanvas!

We spent a lot of time designing the Superpowers platform so that this would be possible :). In fact, Superpowers could even be used to make movies or write novels collaboratively, with the appropriate system and set of plugins.