How far behind schedule is the electrification (infrastructure) approximately?
Err no public statements have been made about how late the work actually is. I believe the original schedule envisaged the route would have been equipped and energised by June 2017 with perhaps some smaller scale testing / snagging during this Summer.
Based on reports here, as I've not ridden the line in months, we seem to be possibly several months behind schedule but that depends entirely on how NR aim to complete the work. If they are able to string and tension the wires on the entire route over, say, a 2 week blockade that might bring things back into some sort of shape. Whether TfL and freight cos can (or wish to) cope with a further blockade is another matter.
With no clarity on how NR aim to get from "now" to "complete" the timescale can't be determined nor can the scale of delay to the operation of electric trains. It's less than 5 months, on the original schedule, to the planned (contractually defined) operation of the first EMU on the GOBLIN. Of course, we have no idea if Bombardier are on time with the 710s nor if TfL have amended the delivery sequence nor how the trains will be tested and brought into service if the GOBLIN route isn't wired in time.