Hi Mark,
60+ Oyster card users already cannot use the card beyond West Drayton. It’s nothing new. The 60+ Oyster card is effectively an off-peak season ticket, so it’s valid to buy a ticket from boundary of zone 6 to Reading and use that in conjunction with the 60+ Oyster.
Even when the full service is running on the whole line next year there won’t be 12 trains an hour to Reading.