I understand from Southern that the new gates at FH and Sydenham will not be constructed until just before the introduction of Oyster PAYG on the line. This is now scheduled for September 2009, which is also when TfL will take over the running of our local stations from Southern.
When TfL take over running of our local stations they will staff the stations at all times when trains are in operation, so that we should expect the new gates to be available for passenger use at all times.
I may have got this wrong so please let me know. My point is that if the above is correct, why should we be concerned - Southern won't be running our stations as from next September, and the new regime of TfL will ensure that gates are usable at all times.