Unfortunately even if they extend crossrail to Reading it still can't
replace all the stopping services because there are 2 stopping
services an hour from Oxford which call at many of the intermediate
stations. So then you would either have to electrify the line to
Oxford (ooh, look a flying pig) or more realistically terminate slow
Oxford services at Reading and inconvenience passengers from
intermediate stations between Reading and Oxford.

Again, see above - those trains won't terminate at Reading, but
provide a direct train to Gatwick Airport, via the fly-under outside
Reading. Didcot passengers will continue to use the HST services, and
yes, other intermediate passengers would change at Reading - either
onto HSTs to Padd or Crossrail.

Ah, that makes sense.

Of course there is
the option of running the Oxford slow services under the wires on the
slows but this would take up valuable crossrail paths and of course
result in more diesels under wires which is a waste of fuel. And no,
I'm not even going to suggest that putting a loco on and off at
reading is a viable idea, because it's not going to happen.

Correct assumptions. Not a chance.

Maybe in the short term they will continue to run under the wires
until more of the Great Western Mainline and branches are electrified
and then they can remove that anomaly.

This is still being worked on by the industry - Twford may well lose
all their fast trains to Padd, as may Maidenhead. It's the only
downside to an otherwise very positive scheme. Whether an HST could
make a call or two is under investigation - an HST already calls
Maidenhead in the am peak, so it's possible with SDO (selective door
opening)

Fair enough

Talking of branches there would
still be the outstanding issue of Henley trains which would almost
certainly run under the wires in the peaks on the slows anyway,
because that branch will * never* be electrified.

As I've said earlier, all the branches including Henley will remain
turbo operated. Henley branch line peak trains may still run direct to
Padd, under investigation still. If they do, they'd change over to
fast lines at Maidenhead. All depends on the extra capacity required
to run at 90mph, rather than 125mph - and if it's considered too
tioght, well, they'll remain branch line services in the peak.

I thought as much. Don't the Henley peak trains already run on the
fasts at the moment? From the timetable they only call at Slough and
Maidenhead as far as I can see.