There is only one good reason to form an all-against-one-party coalition, which is if that party is a danger to democracy. And if the party is a danger to democracy, then the time gained by forming the coalition should be used to start the procedure for banning it.
If the other parties choose to blob together (which they will), they will paralyse each other for a few years and then we'll likely be back where we are now, just that the AfD will probably be even stronger. These coalitions are too broad to deliver what voters want, they're doomed to fail