With ABC their "options" and remit as they were limited by real life and trying to bring it beyond 1968 was flogging a dead horse.
It's not "flogging a dead horse" - to be perfectly honest your mock was just badly implemented. You've already identified the one key area and the second, yeah okay on reflection it probably wasn't particularly helpful but you've taken it as food for thought.
It's fair game to
ABC having won the London weekend franchise along-side Rediffusion having the London weekday franchise. This could have happened and would have been interesting. ABC presumably would have operated out of Teddington, although the IBA may well have forced it to consider maintaining London regional news on Friday evenings, possibly leading to a share/co-production with Redifusion derived from central London.
South Bank was sexy in the '70s, so perhaps in this alternative time-space the Coal Board's pension fund did drag an ITV franchise into its development.