Leterme cannot be neglected: he won the elections in a way almost never seen in Belgium. Without him a government is impossible. But what's going on now IMHO, they are looking for a way to isolate the CD§V-partner, the NVA. They have a separatist agenda and succeed so far to reject the Walloon proposals for a compromise. That way Leterme is taken hostage by the NVA notwithstanding this is estimated less than 10% of the coalition.
A Walloon prime minister is political a non go, really, this is unacceptable for the Flemish(whatever party),so far.
Your proposal of coalition make sense(except of the PM), and in the press simular ideas are already launched. Give it a day or three, I'm sure Verhofstadt will examine this alternatives, and we'll see wich parties will take responsibilities. The struggle of man against tyranny is the struggle of memory against forgetting.(Kundera)
To start with: Walloons don't want further federalisation.