I would imagine stations that already have barriers with Oyster readers
in
place, that are currently only used for season ticket validation, would
be
first. I wonder if they will let these stations go-live before the
equipment has been installed at the intermediate stations.

Its difficult to see how PAYG could work if some stations on the route
don't have readers - it would be a recipe for unresolved journeys.

It happens now with Liverpool Street - Walthamstow Central/Tottenham
Hale/Seven Sisters. It depends if they want to go for some quick-wins like
Victoria-Balham, Victoria-Bromley South or Victoria/London Bridge-East
Croydon. I find it hard to believe Ken would resist the PR opportunity to
go-live on the gated stations early. The press release says work will start
on them first. Will the technology be installed and then left idle while
the other stations have gates installed?