After many days of searching and tests, here's the Beta build of Marshmallow for Locked and Unlocked bootloaders.
This is a beta firmware and it may not work on your device, only way to come back if you are in bootloop will be to flash a stock ftf with flashtool.
1) Better to be on latest Lollipop, so here's a ftf and a flashable zip with recovery:
D6503_Customized ES_1281-4644_23.4.A.1.264_R8C FTF: https://mega.nz/#!MZ9DUQZZ!CqvHIsKxZ...aQtpUFlzTozaXo
D6503_Customized ES_1281-4644_23.4.A.1.264_R8C Flashable, PreRooted with Recovery: https://mega.nz/#!hA102JhS!_GjCQgKO6...OCitrGdPmnFDis
2) Reboot in TWRP recovery.
3) Wipe all (Data, system, cache, ...)
4) Flash the Marshallow zip.
If you have already installed the rom and you've had bootloop or wasn't able to use the phone, flash this in recovery:
5) Flash the NEW bootloop fix: https://mega.nz/#!AJcwERiQ!FUmk6eS5aoVsFSZ1f4WZIELIt7sckPCj11n0AId CNzU
[ROM][MARSHMALLOW][LB/UB][ROOTED][RECOVERY] Official 6.0.1 23.5.A.0.570 | 11/04, ROM for the Sony Xperia Z2
ROM OS Version: 6.0.x Marshmallow
ROM Kernel: Linux 3.4.x
ROM Firmware Required: none
Based On: Stock
Last Updated 2016-04-11