In message , at
13:15:46 on Mon, 19 Mar 2018, Offramp remarked:

I understood what you said about flat fares. You weren't saying THIS
MUST BE THE FARE!! In this computer age there is scope for a Parisian
carnet style product to be put on a card.

Part-time seasons (in effect a carnet) were part of the DfT plan for
National Rail a couple of years ago. It's gone awfully quiet though.

Pre-Oyster I used London Underground paper carnet tickets.
--
Roland Perry