I went through the cascades before for how many units get freed up by each route electrification. If I'm thinking right...
(Lets actually have some maths, rather than pure guesswork!)
Chat Moss:
3 x 156 (Airport - Liverpool L St)
3 x 156 (Stalybridge - Liverpool L St)
2 x 15x / 14x (Liverpool L St - Warrington BQ)
7 - 8 x 185 (Already needed at TPE)
St Helens C
4 - 6 x 142 (Wigan - Liverpool)
4 x 150/156 (LSP - Blackpool N)
Bolton & Chorley
6 x 150/142 (Preston - Hazel Grove)
5 - 6 x 14x/15x (Victoria - Blackpool N)
2 x 150 (All Shacks Bolton, if you do a small re-cast)
4 x 185 (Airport - Blackpool N)
Lancs Triangle gives: ~32 DMUs for NT and ~12 for TPE
With TPE diverting services over the Chat Moss, something will be needed on the Semi Fast over the CLC that is lost.
TPE North Core (With hacking up the timetable):
16 - 22 x 185
2 x 150/156 (Victoria - Huddersfeild)
4 x 150/153/155 Diagrams (Huddersfeild - Leeds via Dewsbury)
2x 158 (York - Leeds Slow)
TPE North to NCL, Midds and Hull, & Selby Links, & via Castleton diversion:
All 185s not used on TPE S and TPE NW and all TPE 170s will be freed up
So a spare pool of 35 185s and 9 170/3s
Then:
2 DMU (Hull - York)
2 - 3 DMU (Selby - Leeds part of the Grand Tour)
The odd Hull - Doncaster via Selby path.
4 x Class 180
1 x HST Diagram
With the allocation I did for the 185s as:
11 diagrams Cleethorpes - Liverpool Lime Street via CLC, Piccadilly, Stockport, Hope Valley, Sheffeild & Doncaster, diverting the current Cleethorpes - Airport service to Liverpool Lime St via the CLC, in the same path, the timings add up.
12 units for the Airport - Lakes & Airport Southport services, joining the services between Airport and Bolton for portion working, freeing a C. Manchester path for the hourly service up to Scotland via Chat Moss.
10 units for the Calder Valley services, ?some extended via the cord to Airport (As required by Northern Hub)
8 units for the Blackpool North - Scarbrough (Extended from York) services.
1 unit for an additional Scarbrough - York shuttle
And if linespeeds for locos can be improved...
3 or 4 units for Buxton - Manchester.
If everything runs in 3 car formation, thats 46 units allocated, 3 maintenance spares and 2 standby spares.
An alternative could be to use the trubostars on Southport - Airport or Buxton - Manchester in place of 185s, the former needing to not be joined to Lakes services, the latter meaning no trackwork would be needed as the 170s can use the SP limits that 185s cannot.
All of the routes I have mentioned would retain the 185s 1st class seating and be branded as 'Northern Citylink' or something similar and retain the same 'express reigonal' service levels, with seat reservations etc.
If the 170s are allocated to Buxton, it gives an extra 4 units for strengthening elsewhere (or Southport for that matter) and theres some pretty peakey services that could use an extra four carriages.
So in total, we're freeing up about 23 DMU from the TPE N / NW, and 40 - 45 from Northern with all the electrification if we have all TPE branches done. So if you add in the extra capacity needed by then, we're proberbly looking at having about 51 pacers being able to go to Rotherham and never return. So thats half of Northern's fleet.
Leaves say, 50 at Northern and 38 at other operators.
In some ambitious proposal within the current GW electrification, if GW get HT's 180s, that will displace some more turbos, and if sense dictates the electrification of the thames valley branch lines, then there should be enough turbos to kick off FGW's pacers, and displace some of their 150s over to ATW, but it will still leave some if you need additional capacity.
Next up, we need a scheme to release DMUs, in a politically popular way, the Cardiff Valleys frees up about another 40 from what I've been told (if you also include Swansea)
So lets say theres 20 - 30 left to find, the Scottish Electrification should cover that if they don't throw their toys out of the pram and actually give some units up...