wrote

even if we leave aside the issue of running into Paddington under
wires, wouldn't having a 100% electric fleet lead to savings in
maintenance and the more flexible deployment of rolling stock. I guess
the total number of trains required for these short branches is pretty
insignificant compared to the Crossrail stock, which will more or less
take over rest of the stopper workings in the area.

When the GEML became an all-electric railway south/west of Marks Tey
(atleast as far as pasenger services were concerned) it initially left
Southminster, Braintree, Romford - Upminster, and Dalston - Stratford -
North Woolwich as diesel-worked branches. The dmus were at life expiry, and
replacement dmus would have needed a new maintenance depot. So the decision
was taken to electrify these lines, Dalston - North Woolwich being
electrified on the 3rd rail dc system and worked as part of the North London
Line. A side benefit was that Braintree and Southminter acquired through
trains to/from London.

It looks as though, when Crossrail opens, Greenford and Bourne End will lose
their through London trains; Windsor Central and Marlow haven't got any
through trains anyway, and Henley will probably make enough noise to keep
some through peak dmus to Paddington. In the longer term it depends whether
other routes served by Reading Diesel Depot get electrified. Reading to
Gatwick already has the juice rail for about 40% of the route. Reading to
Oxford would be electrified as part of any GWML scheme. Reading - Bsingstoke
could well be included if a scheme is developed to get (XC and freight)
electric trains between Southampton and Birmingham. It is however difficult
to see the Berks & Hants line as an early candidate for electrification - I
suspect that if/when electric trains run from Paddington to Exeter/Plymouth
they'll go via Swindon and Bristol.

Peter