So my friend Geoff Marshall (of All the Stations fame) decided to try out some scenarios using contactless out to Brookmans Park. You can watch the video here.
The most important thing to take away is that not only are there no caps for Brookmans Park, if you travel to/from there then the whole fare will be treated as separate to any other cap that you qualify for. It’s actually treated a bit like the Gatwick/Heathrow Express fares, except that the whole range of fares to all PAYG stations are defined.
TfL and GTR say that capping will be introduced sometime in 2020, but I have to wonder whether the same arrangements will apply to all the stations out to Reading when contactless goes live on Jan 2nd. If they do then some people may pay more to travel from Reading and then around London than if they buy a paper travelcard.
Anyway, give the video a watch, and subscribe to Geoff’s channel.