It is not clear whether contactless will be available throughout Greater Manchester or only on the "Priority Lines" If the latter, there will be a number of anomalies where contactless is available at two stations but not on the direct services between them such as
Wigan - Victoria (via Hindley),
Victoria - Stalybridge,
Stalybridge - Stockport,
Stockport - Altrincham,
Ashburys - Romiley (via Reddiish North).
This is actually possible in the London PAYG area, as both Reading and Gatwick have readers but contactless fares are not valid via Guildford.
If there are stations without readers, like Reddish South, it would presumably be possible to have portable readers carried by on board staff, as were used by conductors on the now-withdrawn 15H Routemaster service in London.
Wigan - Victoria via Hindley and Victoria - Stalybridge are both part of the Southport - Stalybridge route. Indeed Victoria - Stalybridge is one of the two lines in the initial 2025 pilot scheme, along with Piccadilly - Glossop. There appears to be an error on the map (post #46), which shows the Stalybridge service routed via Piccadilly and Guide Bridge rather than Victoria and Ashton. AFAIK there are no plans, nor capacity, for a Northern service on this route.
Not included is Wigan - Victoria via Atherton, presumably because the Atherton line is currently served only by longer distance regional services (Wigan - Leeds via Brighouse and Headbolt Lane to Blackburn via Todmorden).
The announcement implies that, on some lines, tap in/out users will be required to use only specific services on that line. "Airport stopping services" appears to rule out not only TPE and TfW services but also the semi-fast Northern services to Blackpool, Barrow and Windermere, for a journey from the Airport to Piccadilly. Similarly for Rochdale to Victoria, "stopping services" implies only the 2tph from Rochdale to Blackburn/Clitheroe (which call at Castleton, Mills Hill and Moston) not the 4tph fast. Applying the same principle to the other routes would mean that for Bolton to Manchester only the hourly Stalybridge stopper would be permitted. And for Stockport to Piccadilly, Northern services from Stoke and Chester would be ruled out, as well as all the Avanti, XC, TPE and EMR services.
I do not see how this service based system could be made to work. Surely simpler to make tap in/out valid for any service, or combination of services, between a pair of stations equipped with readers?