They could do that as BVG has not ruled that out (they stated, it would be constitutional in the last decision, I don't know if they mentioned it, this time, but they won't be able to implement it for 2014, because the nomination process, which is defined by law, has already begun.
The decision is coherent in the streak of emphasizing voters' equality by the BVG in the last years. It struck down thresholds in muncipal elections (it did so as the Schleswig-Holstein state constitutional court, it was by then), it put a limit on overhang seats and struck down negative weight of votes, twice. In smaller decision it also struck down the inclusion of children in the population numbers for redistricting and ruled out the so called "Berliner Zweitstimmen".
And it ruled out the five percent threshold before with arguments that let not much room for this three percent threshold. So it does not come as a surprise for me, the only question was, if they had the balls to stick by their arguments. (I think the desastrous acting of the now and then majority parties concerning the reform of the federal law since 2008 until now and the speed in which the three percent threshold was implemented without any new arguments for it did not help much).
I think, that the creed in stability coming from a five percent threshold applying to only one in not even seven seats of the European parliament is highly overstated in the politician's and media reactions we see now. Many stated today was "a bad day for the European parliament" and that the BVG's decision was "hostile to Europe".
There is a chance, we could see less protest votes in Germany, because until now because of the five percent threshold it was "not dangerous" to vote for such a party. And "prevent the Nazis from getting a seat" has been a well-known campaign strategy meant to attract young voters.
