I don't believe Oyster was ever owned by Barclays, it was owned by Cubic (actually legally TranSys, principally part of Cubic), under a Private Finance Initiative, who devised the actual operation and hold the patents, which have been a source of legal/financial disagreement with TfL ever since. Cubic are a mainstream company in this area, they had previously worked for Hong Kong on the comparable Octopus card, and have since rolled it out elsewhere, such as Sydney, Australia, with the Opal card.
The Octopus in Hong Kong certainly is used for other than local travel - just about all corner shops etc accept it for purchasing everything, and it's expanded further to being the electronic identity card used for entry to offices and schools. It's actually quite difficult to do anything in Hong Kong without one. There were initial suggestions for the same in London, from the days before Visa etc debit cards were widespread, obviously Oyster Shops fitted with the kit would have been the first, as in Hong Kong, but this fell foul of further disagreements between TranSys and TfL. Using Oyster on the Riverbus or Cablecar, just for straight payment, outside any capping etc for the day's travel and not with TfL fares, uses aspects of this technology.