I sort of expect them to switch to facial recognition and do away with turnstiles altogether for most passengers to dramatically increase efficiency once the tech and databases are advanced enough. As in, the system recognises where you entered and where you leave and the fare is automatically deducted from your account. Those who are not known to the system (eg first time users and tourists) aren't allowed enter the station until they set up an account (long term or temporary respectively).
The system would have a bunch of problems but the authorities wouldn't care too much as long as efficiency was high.
