Roadmap

The focus right now is to implement the most critical missing features:

Animation (skeletal, blend shapes, generic script variables)
Audio (popular file format support, music, 3D audio)

These should be finished roughly around mid-2016.

Quickly to follow will be:

Ports for Linux & Mac
Vulkan (and possibly DX12) implementation
Physically based renderer
Website for the community

These are planned for an early 2017 release.

There are many more features planned, but these are without a specific timeline or order:

Mobile render API (likely Vulkan, possibly Metal for iOS)
Android/iOS/WP ports
High level networking (replication, RPCs)
Dynamic global illumination (+ other high fidelity graphical improvements)
Occlussion culling
Terrain
Effects/Particle editor
AI support
VR support
Cinematics editor
Higher level resource streaming support (including level and texture streaming)
Unified shading language
Visual shader editor
More specialized 2D editor features
Script debugging
Level of detail
XBONE/PS4 ports
And more to be decided later...

Implementation times for each of those roughly ranges from 1-4 months.

More contributors mean we can add more of these features quicker. Consider contributing!