Neil Williams wrote:

[Forest Gate and making Oyster touching in & out mandatory for all users]
The problem is the station just isn't physically designed for that. Wall
space in that hallway is extremely limited because of a standalone cash
point, a ticket machine and the corridor/bridge to the main down platform
on
one side and the door to the ticket office on the other. You just couldn't
get enough readers in that would be able to cope with the crowds the
station
regularly gets at peak hours and so we come back to the potential for
lengthy queues as people wait to touch out, shoving and even fighting
right
by a steep stairway and a real possibility that people will take risks and
try to cross the fast tracks to get to use the reader and direct street
exit
there.

Could one or more be put actually on the platform, to be used by
people before they enter the rush to exit?

I'd have to look at the platform carefully to be sure but I suspect not. The
stair case opens directly onto the very end of the platform (give or take
the ramps down to the track level) in open air and trains stop right up at
the front to unload the pax. The platform is an island for both the slow up
and fast down tracks, so there's no wall in this section or anything you can
really mount readers against. You'd have to go for standalone readers and
spread them out so people could get to separate ones but you'd still
struggle to get enough in the limited space available and no way are you
going to have enough that could cope with an evening rush hour crowd of
newly released sardines - you will still get a lot of people trying to use
very limited facilities and this on an island platform that has fast trains
running down one side.

(The down platform is different as the station is in a cutting and there's a
huge wall that you could put readers up against, plus you tend not get huge
crowds in one go on that side, give or take West Ham home match days, so you
wouldn't need so many. The fast up platform is generally used by stopping
services during late evenings and weekend engineering works so doesn't have
much passenger traffic.)