In our political system we form our coalitions before elections. What you are suggesting is a system that forms coalitions after elections which you see in some European countries. This is such a drastic change that I doubt one would ever see it here.
Another popular liberal dream is to establish a true "democratic election" by getting rid of the electoral college. These are the same people who devised the proportional delegate allocation and the superdelegate system for the Democrat party and for the entertainment of the rest of us. Ain't gonna happen.
In our political system the coalitions are well established no matter who the candidates are. The election is not particularly relevant to the coalition process. That is why a third party would have to build after an election since there is not an established infrastructure for it.
As for the removal of the Electoral College, I believe you will find that, depending on which state is pushing it [or when - 1993 or 2001 as two examples] desire for change is pretty evenly split between the parties.
On the other hand, if you feel a system that was intended to "carry the voters wishes" to the Capitol at a time when technology did not allow timely counting of votes in a national election to be more significant than true democracy of 1 person, 1 vote, so be it. But I am not sure that is a "liberal dream". I think that is a dream of Democracy [you know, that idealism we tell everyone we believe in and push to the world.
And as for the Superdelegates, I could not agree more. It is a braindead system.
Your vision of the Electoral College might be clouded by its use by Bush to gain the Presidency even though he lost the popular vote by 543,895 votes. It's OK, he made up for it by being the least popular President in HISTORY.