The core operating system and tool-chain for Tizen 3.0 is expected to be updated. With that will also come Tizen 64-bit support, which makes sense since by the time of Tizen's 3.0 arrival there should be ARM64/AArch64 devices available in the market.
Tizen 3.0 is also expected to add protected multi-user support, a new 3D user-interface framework with a new rendering engine, a dynamic animation library, a Wayland-based compositor, and the Crosswalk HTML5-based application runtime using the Chromium/Blink engine. Tizen is going with a Wayland-based compositor as it's a "simpler replacement for X" and a "light architecture, better performance, smaller footprint."
These Tizen 3.0 details were shared during the Tizen Developer Summit in Seoul, South Korea. The Tizen 3.0 slides are available via TizenExperts.com.