The Sony Xperia Z2 has official CyanogenMod 11 (Android 4.4.3) support starting from today. The first nighty build for the handset, codenamed Sirius, is now up on the CyanogenMod website.
You will need to have an unlocked bootloader if you want to give the custom ROM a try, although as it’s a nightly build don’t expect it run as stable as your current daily driver. Current issues include bugs with the camera (interface freezes while touch to focus) and touchscreen responsiveness. Hopefully, over time these issues will be ironed out.