xPosed Installer on HTC One M8
After performing a full backup of my phone, I went through and re-rooted (not too sure the actual steps taken as I used the same method), and then reinstalled Xposed.

After validating root access via SuperSU and that the default setting for updating applications was retain root access I went ahead and used the "install via recovery" method, which succeed (I used the .zip for Android 5.0). Then lastly I ensured I performed a soft reboot rather than a normal reboot (although I would have assumed the default reboot option would be that of a soft reboot to ensure Xposed started).

So there we have it, another PEBCAK move by me - ensure you soft reboot and do not let the default reboot take course