I do however question the wisdom of Preston unless it came with massive housing development and a few new stations, as it's really very rural north of Burscough. To me reinstating the curves and running Merseyrail to Burscough Bridge with the Ormskirk-Preston becoming a Southport-Preston (could be done using the 2 units it presently uses) taking in the halts to allow a more consistent pattern on the Manchesters would bring far more connectivity benefits than running unsuitable urban units without toilets on a rural branch line. In that case I'd favour third rail or battery.
I hope you don't mind me taking inspiration from your idea:
Extend Merseyrail to Burscough Junction with batteries (for now.)
Like you said, send a service from Southport to Preston via Burscough N-E curve (adding a station at Midge Hall with a passing loop for the token exchange, why not?) allowing Southport/Preston travellers to avoid the main line *and* access Merseyrail!
Extend Merseyrail to Skem via Rainford with OLE (it's
so much further than the relatively minor Ormskirk to Rainford Jn distance) and terminate the Wigan service at Rainford.
Then, OLE could be slowly extended back towards Town if the 3rd rail decision is finalised (i.e.
never to come back, despite some people's wishes)...
which I'm certain is already the case today.
What do you mean by this?
running Merseyrail to Burscough Bridge
Would this really happen? Unless there were platform(s) on the S-W curve, Merseyrail services would block the line; and the cheaper option of terminating at Burscough Jn then telling people to walk would almost certainly be picked.