After the timetable change, what are the options for getting back to stations beyond Reading between 1600 and 1930 if you hold an off peak ticket ?
Looks like:
Buy a ticket not priced by GWR (e.g. Newbury to Potters Bar)
Use Waterloo (although that isn't clear and doesn't deal with connections West of Reading)
Use TfL Rail (although that isn't clear and doesn't deal with connections West of Reading)
Wait
I don't quite understand what is implied by the way the ticket restrictions are set out in BRFares - it isn't a blanket restriction but at the same time the gaps aren't quite right for TfL Rail services.
GWR booking engine shows off peak tickets from / to Reading valid on 1613, 1628, 1713, 1813, 1913 TfL Rail services but not others. However, that doesn't really make sense with the gaps in the times in the BRFares information. They can't really restrict the TfL Rail services because there is no restriction for travelling from stations further West from Paddington within the travelcard zones.
Not sure how it will work further West because not only are the trains restricted from Paddington they are also restricted from Reading. Strikes me that this is effectively intended as a full blanket restriction.
The GWR booking engine also suggests that the 1742 and 1842 services will be available for off-peak tickets. These appear to be 387s running Reading and Didcot only.
I would assume that a blanket peak fare will apply from 1600 to 1900 on TfL Rail using Contactless (determined by where you first tap in).
Hopefully they publicise widely what is intended and whether it applies just to tickets to London or whether also to local destinations - e.g. Newbury to Reading or Newbury to Maidenhead. Two months out they should really have publicity available about this change.