Once the current round of electrification has been completed there will be hopefully a set of experienced overhead wire erectors and all the required equipment looking for something to do. The MML is I believe a favourite because it is relatively self contained.
They could wire the whole thing first then replace all the trains in one go with new electric. Or, they could do the Bedford to Leicester bit first and add pantograph coaches. IIRC every EMT service stops at Leicester so that is a suitable place to raise/lower the pantograph while while the rest is wired.
The other question is what about the services that run on from Sheffield to Leeds and York. If XC are already fully equipped with bimode trains that doing that extra bit would extend their use of the wires down as far as Derby which would then surely be a short step to filling in the gap from Derby to Birmingham New Street.
Once the whole of the MML is done (the summer Saturday extension to Scarborough would presumably have to be dragged or abolished) the bi mode 222s could then be replaced by new pure electric trains.
The increased but far from total overhead wire cover of the country must mean that there would be plenty of services that would benefit from second hand bimodes. I.e Nottingham to Cardiff or some of the transpennine routes
