I was at the same meeting as andrewr and although we still need confirmation, I do expect that TfL will operate the gates including PAYG tickets from September this year.

Other train operators will take longer to allow for using PAYG.

We could find ourselves in the position that you can travel to London Bridge by PAYG Oyster only if you change at Canada Water to the Jubilee Line.

There are bound to be a few perculiarities in the early days, but in my opinion it is well worth it for the increase in train services and being part of the 'tube'. We will have some PAYG service before other Network Rail stations.