I suspect those outboundary locations where the price differential had increased considerably making these tickets particularly relatively cheap - such as from the South Coast - will be finding the fares will rise to match the standard elsewhere, i.e. the price of a return to the boundary plus the Travelcard element.
Out of interest, what is the current average fare for the Travelcard part?
A quick skim of a few fares for around here shows the travelcard differential at:
Cambridge : GA-only weekend : £5.80, any permitted weekend : £7.90, any permitted off-peak weekday : £9.70
Ely : any permitted weekend : £8.10, any permitted off-peak weekday : £9.60
Kings Lynn : Any permitted weekend : £7.80, any permitted off-peak weekday : £8.30
which all seems a bit scattershot, but GA-only fares apart, around £8 at weekends and £9 weekdays.
Is that typical?