Pretty much since the 2011 vert was introduced that's what's been used. It makes since since these cars are used in the 500 Festival Parade as well as driver/VIP laps right before the race. Easier to drop the top and sit people in the back.
2010 may very well end up being the last year the 5th Gen coupe had a Pace Car Z4Z package! I was hoping to see 50 - ZL1's here someday - not sure that will happen..