Welcome from Germany! As someone who's had his wife go flying off the back of the rocket, can't see where handholds would be beneficial. Just cause they're on the bike doesn't mean they get used! My wife didn't fly of the back because there were no handholds...but rather because she wasn't holding on to what was available (combined with a pretty high torqued machine!) Experience is also no guarantee...I've been riding 25 years and she's been riding over 7 at the time. Both with multiple MSF courses. Sometimes accidents happen; that's what makes them accidents!
That's one reason I've got a solo saddle now, and I'll be darned if I'm putting handles on the back for a ghost rider.