Beware the Ides of Opinion Polls or does The Economist never learn? The result of the upcoming election in Germany will not be known until the last vote is counted.
Government formation thereafter is more heavily influenced by small changes in party representation. There are direct members, list members and adjustments in an election where there are overhang seats and everyone has two votes with different methods of counting them eventually giving rise to a result.
The present grand coalition surely arises from Mrs Merkel's desire not to be hidebound by opposition politics because in the last election the CDU/CSU did not have a standalone majority of the seats. How is Mrs Merkel now expected to "win"? She will be elected in her own constituency first. Remember that this time last year there was an upset there for her party in the regional election where the CDU was beaten by both AfD and the SPD.
I am not writing off the possibility of gains on the day for the SPD. Going into coalition government with another mainstream party is not, in any case, a defeat in a coalition system. Sooner or later Germany will need a bit more spark than just keeping quiet and not upsetting anyone. Its infrastructure spending needs and urgent requirement to upgrade its defences in an unstable world will need hard decisions and Martin Schulz can make them.