My phone is rooted, and I tried to remount the system partition in a terminal emulator like so:
mount -o remount,rw -t yaffs2 /dev/block/mtdblock3 /system mount -o rw,remount /system
Both commands gave the output:
mount : read-only file system
Because of that I can't install Busybox, Xposed, etc. I'm using Android 4.4.2.