If Gillard was to lose the next election, in all likelihood she would step down as leader. Kevin Rudd would probably win such a leadership vote then. Shorten wouldn't have the numbers. Albanese is of the left and wouldn't have the numbers. Only other possibility would be Stephen Smith.
You know nothing of inner labor factional politics. You say Albo is a member of the left and that rules him out, at the same time a member of the Ferguson left sits on the throne. He wouldn't get it because, well, he's not a contender, why did you even bring him up? Jason Clare has a bigger chance of leading the ALP than Albo does.
On what spaced out, loony basis do you come to the conclusion that Shorten is likely to be bested by Rudd in caucus support? At the moment Rudd would be lucky to have thirty votes in a leadership spill against any member of the frontbench. He ticked off the factions, don't you get that? They can shape the bulk of leadership ballots. Only one member of the NSW right did not endorse Julia Gillard and she was forced to resign immediately after or get rolled in preselection. (Julia Irwin). Smith would be a serious leadership contender if they lost the next election no doubt but you mention him like some afterthought "it's never gunna happen" type of canidate. And no he isn't the only other possibility, if your calling Rudd and Albo in the mix then the obvious name is Combet you dunce. .