A search on:
schwarz grün bundestagswahl (schwarz being the CDU and grün being the Greens) reveals extensive speculation (in German) about the chances of a coalition between the two parties as a possible outcome of the German general election this September. I think gay marriage is a big thing with the Greens and CDU agreement to it might be a prerequisite for a coalition.
What follows here is off-topic re gay marriage but is related to the coalition theory:
Green dreams of a coalition with the CDU in the Bundestag may also explain what is happening in Stuttgart.
Baden-Württemberg elected a Green Minister-President (the Greens are the senior partner in a coalition with the SPD) in March 2011 and the city of Stuttgart recently elected a Green mayor after many decades of CDU rule.
Both of these developments were driven by voter discontent with the Stuttgart 21 project to turn the city's terminus station into an underground through station.
The whole Stuttgart 21 (S21) thing is a big real estate deal and was very much a pet project of the CDU (especially the former CDU Minister President of Baden-Württemberg, Günther Oettinger who is now EU Energy Commissioner) with SPD support. Over the last three years, the campaign to stop S21 has uncovered huge failings in the planning and financing of S21. The new station was sold to people as having a greater capacity than the current station - in fact it will be much lower. The fire safety arrangements are hopeless, the geology of Stuttgart makes tunneling risky and expensive etc.
A few weeks ago, Deutsche Bahn finally admitted that S21 would cost 6.8 billion euros rather than 4.5 billion, the latter figure having previously been presented as the absolute break point, above which the project was no longer viable.
Insiders say the true cost is more like 11 billion euros.
S21 therefore looks like an even more expensive disaster than the new Berlin airport, the difference being that the airport is more or less built while S21 has hardly started (no tunnels have yet been dug) and could still be stopped.
Given the Berlin debacle and the upcoming election, you would think Merkel might want to discreetly drop S21.
But no, she has said that the extra 2+ billion euros will be found. According to Deutsche Bahn, some of this will have to come from the Land of Baden-Württemberg and the DB is ready to take them to court to get it.
Merkel was given a rough reception on her last visit to Stuttgart (beware, video is quite noisy) and I think she wants to 1: teach them a lesson and 2: show the rest of Germany that "the street" will never prevail (even if it's clear that it was right all along). I think she has also been quoted as saying something like: "how can I tell the Greeks to get tough and ignore street protests if I can't even manage to do that in my own country".
You would think that the Greens (elected on the back of their opposition to S21) would be making the most of this situation to kill off S21 once and for all (by highlighting the technical/safety failings which never get much of an airing in the national German press).
They are making some of the right noises, but it looks as if they are holding back, possibly with an eye to the general election in September.
The Deutsche Bahn Supervisory Board is meant to make a final decision about Stuttgart 21 in the next week or so.
As the government told them last week that they would not have to worry about damages resulting from legal action (brought against them by S21 opponents accusing them of negligence if they allow S21 to go ahead in the face of overwhelming evidence that the whole thing is a massive fraud), it looks as if Merkel will get her way. But she can expect to be plagued by Stuttgart 21 protests throughout the election campaign.