Prevent the war, as has been suggested.
The original design however was limited. You would end up with the development of Belconnen, Woden, Tuggeranong etc once initial development stalled in 1970s. By the looks of it, maybe theres more development on the South of the river as well.
It also seems that the original plans had a railway going up through civic along what is now Constitution Avenue and then heading north along Torrens Street to marshalling yards further to the North. It still has the same stupid design of Northbourne Avenue hitting London Circuit which will still lead to the bad traffic...
Not sure if it included designs for trams, but they would be good to have (still waiting a 100 years later for them...)