There are many aspects of this scheme that will only become clearer over time. It is already envisaged that wires will not reach Sheffield until 2020 - CP6.
If the electric spine is going to provide sufficient capacity for freight the four tracks north of Bedford that were present in the 60's will possibly require re-instating. The double track section south of Leicester to Kettering together with traffic going east west through Wigston Junction will be a bottleneck in time.
The diversion routes Corby to Syston, Trent to Clay Cross & the old road Chesterfield to Rotherham (with connection to Sheffield via Woodhouse) will hopefully be announced in due course
The Electric Spine as it stands is a dead end! - yes the next stage hopefully is to electrify in CP6 to Doncaster/Moorthorpe - the teams are likely to be in this area to continue this work. The Tram Train project will not interfere intially if the Rotherham Masborough route only is electrified, this being the intercity route.
The other anomoly is why a IEP Depot is being built in Doncaster - at present this is 30 miles at least (Leeds) from journeys end on the East Coast route so a lot of ecs mileage must be envisaged unless this is then to be a base to provide IEP stock for Sheffield services?
Time will tell - the volume of work announced already could not be completed in CP5 so a rolling scheme no doubt will emerge.
You are right about the electric spine project unfolding slowly. I'm not sure it has yet been though through properly.
If you have a team electrifying the TP route around Leeds, why would you not get it to follow that with work on the MML scheme south of Sheffield (and the fill-in routes later)?
The current plan seems to be to start at Bedford and work north, leaving Sheffield till last.
The train plan and future franchising setup for MML, E-W and West Mids-Thames Valley after wiring is also unknown.
The DC-AC conversion is still a complete mystery, with local SWT/NR disinterest, and no support from the freight guys.
Too many unanswered questions. I wouldn't be surprised if NR pushes to defer the conversion, and concentrate on the work north of Basingstoke.
Doubling the old MML 4-track sections is pointless unless the traffic flows have been thought through (ie a proper business plan!).
I would say the only nailed on upgrade would be Wigston-Syston because of the clash between the MML and the fast-growing Nuneaton-Felixstowe freight traffic.
And I think it would be wrong to wire long and lightly-used diversionary routes when you would get a better return from wiring much busier
routes elsewhere.