Yesterday TfL announced their initial plans following takeover of the GWR suburban services between Paddington and Reading on December 15th. In contrast to any other TfL takeover, neither Oyster nor contactless will be available on day 1. To ensure a smooth introduction, contactless PAYG will be introduced from January 2nd 2020.
The big news though is that Oyster PAYG will NOT be valid between West Drayton and Reading. This means that adults with railcards, 11-15 and 16+ zip card holders will not be able to make use of PAYG. And holders of Apprentice, 18+ Student and Jobcentre Oyster cards will not be able to seamlessly transition between using a travelcard stored on the card to PAYG. On the plus side, under 11s accompanied by adults will be able to travel free, but only on the TfL Rail services.