I'll test it!
Edit/Update 1 : Wowzer guys, I have some good news for you all, I have been successfully able to downgrade from 4.4.2 to 4.3 without any issues, The firmware I downgraded to is MI3 and Knox is not present in download mode will post steps soon and guide you through steps for a safe downgrade, PS : this is only for SM-N900/N9000/Exynos for now, screenshots attached..
Edit/Update 2 : Steps to Downgrade (Note 3 Exynos only!)
1 - Download the bootloader.zip and extract then flash in Odin. (Find in attachments) (don't select any other option in odin except F reset time and auto reboot) (are selected by default).
2 - Download any 4.3 JellyBean Firmware from sammobile.
3 - After flashing the bootlaoder reboot into stock recovery (power+ home+ vol up) and wipe data/factory reset and cache partition
4 - Turn off the device and reboot into download mode and flash the 4.3 Firmware in Odin.
5 - After flashing completed let the device boot till boot screen and pull out the battery and turn it off then turn it on again and reboot into recovery (power+ home+ vol up) and wipe data/factory reset and cache partition once again and reboot and let the device boot up.
That's pretty much it, you've safely downgraded to Android 4.3 from 4.4
This is only for Note 3 Exynos!
I'll be testing some work around's for the N9005 (Snapdragon) to reset Knox/Firmware Downgrade once I get that device as I have given mine to a friend, and have been saving money to buy a new or used N9005.
I have a N9005 with me reactivation lock = on and knox 0x0 if you have some news we can test on this one.
I can vois the knox on propose and test any solution on it.