The first plane in for mods usually take eons. In this case, the plane was supposed to be ready in December but then they apparently cleared the IFE for installation, so, this has only added to the delay.
I remember when UA's first reconfigured 747s and 777s were done, it also took a few months for the first plane to be done since the new seats and IFE meant that FAA had to re-certify a few things which made the delay worse.
In the end though, it shall all be worth it as we shall we will have a plane with nose to tail AVOD and the nicest seats in the fleet in all cabins.