I am curious to know as to whether a smart card could be theoretically used across the rail network? For example, both SWR, TfL and C2C use ITSO compatible smartcards. Is it possible to buy a through ticket on the Smartcard all the way from Guildford to Southend for example? Similarly, GTR also use ITSO SmartCards - might it be possible to use the SWR smartcard from Farnborough to Bedford?
In an even better world, if one were to have a season ticket on a smart card, it should be possible to pay a "top up fare" if crossing the season ticket zone made up part of the journey.
I am not aware of any current plans to introduce this. Your suggestion makes perfect sense and it would make ticketing much easier for everyone involved.
The DFT produced a "Strategic vision for rail" which says...
Unfortunately we all use different software and hardware for smart ticketing options but if all trains operating companies aligned it is theoretically possible - it would probably come down to the DFT stipulating and implementing a piece of national ticketing software so it all worked together.
Train operating companies are starting to work together more on projects, especially around making the customer journey easier - so watch this space.