I have SUCCESS ROOT + SuperSU + Xposed on my Cat s40 :]
1. Kingroot root
2. install "SuperSU_v2.65.apk" ( i installed it by Lucky Patcher as System app)
4. use script "switch_armv7.sh" i added script i found that on XDA forum but i don't remember where.
If script don't work you can try again gain root by kingroot and in SuperSU update supersu binary ( SuperSU can detect Kingroot so you must uninstall it) This script worked for my Cat s40 fine.
5. After script install new binary in SuperSU app
6. SuperSU succes!
7. FlashFire flash Xposed Binary ( i added too Xposed binary)
7. Reboot ( boot is longer than normal)
8. You have SuperSU root and Xposed Framawork on your Cat s40
You can too by FlashFire make backup your system partition and use it in TWRP if someone do it for us... :P or flash it after gain SuperSU root ( FlashFire on Kingroot don't working)
You do it at your own risk!
First i tried that method on myPhone Infinity LTE ( i can that flash by computer when it bricked )
I think it can work on all Android 5.1 lollipop.