Why organize a class action suit against Steinberg - after all, it is the Apple OS update that has killed the plugs, not anything Steinberg/Yamaha have done & this is an all too common issue with Apple OS as every single time they “update” their OS, things fall apart and not just from Steinberg either. We have heard this so often from Mac OS/Logic/ProTools users as well, where an IOS update kills off either Logic or ProTools compatibility and they have to spend several days getting everything working again and nobody ever seems to point the finger where it should be pointed - Apple’s aggressive business models that would certainly end up in court of Microsoft tried it on.
You say that “we can send our complaints to Steinberg as that where we bought our product” yet it seems to me that the product causing the problem here is the Apple OS and their insistence that you constantly “upgrade” it every few months to yet another rewrite of OS-X. Try writing to Apple and threatening them with a class action suit instead, perhaps, and see what kind of a reply you get back as after all, it is their code causing the problems