I reckon they have thought of electrifying the Midland at least 4 times in recent years. There is little point, unlike the East Coast which is relatively straight, the Midland winds around all over the place, so speed is limited by the track formation more than the speed the trains are capable of.
Electric only trains are also a liability in bad weather, look how many times they are delayed by having to slow down when the wind picks up, to say nothing of the total chaos when the wires come down. With the recent hikes in electricity prices the cost of running them has caused issues, indeed one freight company recently laid up its electric fleet as it was costing too much to run them!