YMMI has definitely been fitted. I think it was this thread where I linked to Ian Grinter's photos on Twitter regarding the 787s. Well, he's done it again by photographing YMMI leaving Cardiff earlier today in such a way that we can see the wifi hump.
I don't know if it was fitted on this visit or the previous one as he didn't photograph it when it left CWL last time but it's there now.
In other news, we now have the A350s coming in which are the first aircraft to join the fleet with wifi factory fitted. I'm wondering if there's any noticeable difference between the Panasonic system they're apparently using and the Gogo system on the other longhaul aircraft. I await reviews in the coming months...