BMW had made some bikes with twin spark - BMW R1150 - a few years ago. Here is what it says about the reason of using a twin spark.
"The standard R1150GS model was produced from 1999 to 2004, when it was replaced by the more powerful and lighter R1200GS. The Adventure, which was produced from 2001 to 2005, was replaced by the R1200GS Adventure in 2006.
In late 2002, the optional ABS system was replaced with an electrically servo-assisted combined braking system. In addition the engines were equipped with twin spark plugs on each cylinder to improve emissions and improve a persistent surging problem that affected many BMW boxer models."