The TfL plans to expand the implementation of NFC payments next year to other public transport systems, including the London Underground, DLR, London Overground and trams, and even the national rail network. For now, the TfL will not push a daily cap limit on spending.
However, once the NFC payment system rolls out to other transport systems beginning next year, a cap limit per daily and weekly basis will be introduced. With regards to any potentional fraud issues that may come along, TfL says that the service will be handles by card providers. Basically, ticket inspectors will be asked to get a print out from the bus driver, which will be verified during the actual payment transaction.