This press release states that "Passengers using the technology will be able to use their bank card or smart device to tap-in on station readers in the knowledge they will automatically be guaranteed the best price available on the day of travelling".London NorthWestern Railway have issued press release about 14 of their stations getting it, I assume Milton Keynes Central is not one of theirs.
Fourteen London Northwestern Railway stations to receive Pay As You Go upgrade
Fourteen stations operated by London Northwestern Railway (LNR) are to receive upgraded Pay As You Go technology as part of a major £20 million government...www.mynewsdesk.com
We know that is absolutely not true if two fares structures are applying concurrently, particularly with railcards, time restrictions etc.
This quotation from Huw Merriman is somewhat ambitious. "By removing the stress of finding the best deal in advance or having the right ticket ready to go at the barriers, the extension of tap-in tap-out ticketing is the next step of our plan for rail reform and we’re working towards Pay As You Go being rolled out beyond the South East through the Midlands and up to the North."