There was talk about open sourcing the code some years ago, but in the end it wasn't possible because there are certain parts of the engine which are proprietary third party code, which cannot be released as open source.

And to stay on topic, there are newer engines with WebGL support, so if somebody wants to do some 3D stuff for web browsers, it's maybe a good idea to check out game engines like CopperCube: https://www.ambiera.com/coppercube/