So, the acid test will be whether this is used as a way of bringing TfL's fares system to the full Oval area, ie a cover for scrapping the current one. Remember that TfL don't like Cheap Day Returns (although back in the golden years pre UTS, they used to offer themselves) or breaking journeys. They also have their own, shall we say, unique approach to child fares, particularly complicated for those in the 12 -16 range, ie. there are reductions but you have to have special card to get them so if you don't live in London in reality there aren't any. National Rail allows children half price without prior authorisation, of course.
Currently, within today's Oyster fares area, the two systems (sort of) co-exist. It creates hours of fun for me trying to explain to my brother (who lives abroad) how his family can get around on public transport at minimum cost depending on where they are going (we have choice between LUL, LO and ex-BR here) but, honestly, for normal people it is all a bit weird, isn't it? However, if we are bringing places like Stevenage and Cambridge into Oval and are then are thinking of scrapping CDRs, meaning higher day out fares in practice, and making the tourist's kids pay full price we may find a little bit of opposition out there....!
Of course, since Oval just moves the processing to the back office it could be set up to continue to offer CDRs, even those to London Terminals (which offer choice of termini stations to use, different one out than back).... but do we think DfT/TfL are really up to the challenge of doing this?