Kathrin, I will post this on our Facebook page and see if you can get your question answered. Also a good idea to post this question in the instructors corner!
I'm a professional singer and Pilates instructor and have been wrecking my brain over this one for a day now. Frankly I don't see any reason why a class for singers should be any different from a regular mat class. Better posture and core muscles will improve breathsupport needed for singing. Singers maximise breathsupport by breathing into stomach, back and ribs. As Pilates uses only lateral breathing, they could possibly be a bit fussy about using breath in a "limited" way, worried it might effect their singing. (I'm thinking this could be a case for classical singers especially.) However, it's easy to switch between the 2, once you familiarise yourself with it. Singers are "professional" breathers.
The other thing is the "scoop". In singing you need to release your stomach. But I see no problem in scooping for an hour during Pilates class and then releasing again when singing. After all, Pilates gives you better control over your muscles. Why not do what you always do and put the label "Pilates for singers" onto it. Very interested to see if other perspectives will be posted.
Thank you Barbara for your suggestions. In fact I have some singers in my classes and they have told me that Pilates has helped them to improve their capacity to use the voice. That's why they've asked me to give Pilates classes to their colleagues. But I think you're right: The method is good, not the exercises on their own.
This is a fascinating topic; I studied singing early in education and still sing some in my spare time. I totally agree with what Barbara has posted above, and feel that Pilates has helped me to gain control (and release) of very specific parts of my body and improved my singing very much. I think it would be interesting to develop 10- or 20-minute standing Pilates sequences that a person could do either just before performing or as a break from practice that would help activate the body (even the legs and feet are important in singing well!). You may be right, though, perhaps the best thing would just be to practice "normal" Pilates. It helps everything! :)
I've found some interesting articles on the internet: www.pilates-pro.com the article is "pilates and the voice". The other article has the following title: "Pilates training and the actor/singer" by Joan Melton. They're quite interesting.