I've been back button focusing with my XT1 since I got it 18 months back. But ... with back button AF-L used for focusing (have it set to only focus when I press the button) ... the camera still has the shutter half pressed focus enabled. I think this new XT2 firmware will give the option to completely remove focusing from the shutter button. So a bit different if that is what you are looking for. But with the XT1, when holding the AF-L for back button focusing, the shutter response to the shutter button is instant ... as it should be.
On the XT1 the back AF-L button for back button focusing only employees contrast focus, not the phase focus. So the AF-L can commonly take longer to lock focus. It is a nuisance and disappointing. But on the XT2, the AF-L button now uses the same phase detection focus so it is just as quick as the focus via the shutter release button.