It is an interesting observation that both of the last two leaders of the Liberal Party have been considered possible ALP recruits in the past.
Tony Abbott was certainly wooed in his student days by great NSW right winger Johnno Johnson. The fit would have appeared natural because Abbott's primary opponents in student politics of the 70s were real communists of various varieties. As such he was a natural ally of the former groupers who retained control of the ALP. (See note below).
The fact that he ended up in the Liberal party can be partly credited to the influence of the future Tanya Costello, though not by the mechanism that Bob Ellis claimed in Goodbye Jerusalem - the "seduction" was entirely of an intellectual kind.
Malcolm Turnbull was also touted as a potential waverer, especially through his closeness to Paul Keating and his support of the Republic. In his case the presence of his father-in-law would have been a steady influence on his choice of the Liberal clan. But the facts remain that at every turn Malcolm has had to impose himself on the party, they have neber embraced him. This perhaps reflects the deeply anti-intellectual traditions of Australia's conservatives.
It is not unusual for individuals to be intent on politics but unsure of which path to pursue. It was always an accusation made by my parents (who knew the Whitlams at University) that Gough only went to the ALP after being unable to gain traction on the conservative side. While history records the progression otherwise, it is notable that Whitlam's commitment to the ALP was about modernising the constitution not any philosophical cause.
By the same token ALP history is replete with "rats" who broke with the ALP to side with their opponents - the most notable being Billy Hughes and Joseph Lyons.
None of this should be surprising given the way "public choice theory" argues that democratic politicians are really competing for the same median voters.
Today we see the suggestion that Turnbull is a threat to both Abbott and Gillard - posing the question of what support Turnbull would have as Labor leader. Given the fact the ALP has been attacked from the left by the Greens the party is increasingly a party of the social democratic middle. The Liberals are still highly fragmented, but Abbott is certainly a poster child for "do nothing" conservatism - a position which the more rabid right can accept.
The Gillard coalition looks fragile given the ongoing demands from Andrew Wilkie that Gillard has to use all her political capital to ensure the pokies legislation gets through.
It does raise the interesting question - what would Turnbull do if a deputation from the ALP factions - possibly including the PM herself - were to say "Malcolm, the most important policy challenge before us is getting to progress on climate change. You know and we know that if the Government stumbles, then Mr Abbott will become Prime Minister and climate change and all other good works are at an end. We invite you to change sides and to be Prime Minister ...."
Note: The SRC of which Tony Abbott was President (directly elected) had 21 members (by recollection) that were made up of seven members of the broad left, seven members from Abbott's conservative ranks and seven members of a much less co-ordinated middle. Members of that middle identified variously with the ALP, but included a zionist group that was motivated by opposition to the pro-Palastinian stance of the left.
I was elected Vice-President, Paul Brereton (now a Justice of the Supreme Court of NSW) was elected Honorary Secretary/Treasurer, Tanya Costello (nee Coleman) was elected as Education Officer. I would need to do more research to do justice to the full list.
Novae Meridianae Demetae Dexter delenda est