I'd expect it to last till August/September time as the P14 issue effectively disappears when even a tiny bit of through running starts from the west as Paddington High-level platform availability and options then improves overnight.They’re diagrammed to work Hayes services all the day I believe with the same two units booked to stay there. The peak extra trains into P14 are I believe peak only diagrams that come from Old Oak Common and back again. Hayes & Heathrow stay at 2tph in the peak - it’s only Reading that goes up. I know a few sets rotate in the day, but normally they are Reading diagrams.
The issue would presumably be giving mileage to the 7 cars - both the first Up Heathrow makes the first Down Hayes service (which would need to be 9) & more diagrams available for Reading trains. Ultimately though if this is all temporary for just the short/medium-term it’s not too bad but those Reading trains can get rather busy.
Some of the Readings need the GW timetable revision for through running, hence some still running in the HL platforms for a while after that which given time lag from the start of through running makes it ideal to have the 7cars on Reading as it allows time for a "slow" (1 at time) conversion programme keep as many units in service as possible (given inefficacies of not through running on unit requirements).
