Upvote:2
When it comes to point to point fares like this, the zones are only really binding when it comes to paper tickets or Travelcards - if you have a validated pay as you go Oyster card or contactless card then there would be no way for a ticket inspector between Clapham Junction and Richmond to know if you intended to leave the train or to change when you got there, and having a validated card means you have a valid ticket to travel (which wouldn't be the case if you were at Clapham Junction with a Zones 3-6 Travelcard, for example).
Condition 7.2 of the Conditions of Carriage (http://content.tfl.gov.uk/tfl-conditions-of-carriage.pdf) makes a distinction between "a ticket that is valid and available for the journey you are making" and "a validated Oyster card, Oyster photocard or other smartcard, when you are paying as you go, showing a record of the start of your journey [or] a validated contactless payment card", which would tend to agree with the idea that Oyster or Contactless fares are valid between station pairs, with or without intermediate pink validator touches, regardless of zones - but then Condition 7.3 gives an exception to this if it is believed you are trying to defraud TfL.
If there was engineering work on the Kingston loop and the only available route to Richmond was via Clapham Junction, it's not clear whether the "avoiding zones 1 and 2" fare would be available for journeys via Clapham Junction and Richmond (there's no upcoming work on that line that I could find in order to check).
The most correct answer is that it's not really valid - but there is no practical way for anybody to know if you got to Richmond via Kingston or via Clapham Junction. However, if you're suspected of trying to get a cheaper fare than you should pay, then you may have your Oyster or Contactless card removed or banned from the service.