~ How many Chiltern stations would it cover, all of them, or just those
closer to London?

TfL have aspirations to introduce Oyster PAYG as far as High Wycombe,
and possibly Princes Risborough / Aylesbury:

http://www.tfl.gov.uk/rail/downloads...dary_May06.pdf

Dorridge to Stourbridge will be covered by Centro's smartcard:

http://www.centro.org.uk/source/WMPT...March_2006.htm

Chiltern's aims for London - Birmingham journeys seem to be focusing on
e-tickets and mobile tickets, which just leaves Dorridge/Stratford -
High Wycombe, which i can't see much effort being devoted to.