Give me an R mount camera, I hook it up to one of the signal analyzers, and in ten minutes I will have a record of all the signals being exchanged between lens and body.... Then, you decode the signals... it is a very easy task with the right equipment, and it is almost inconceivable that Sigma, Tamron, and the others can not do this
I would be very surprised if Sigma/Tamron/etc cannot reverse engineer the codes. But, it is something I am watching. Even with the existing EF electronics, my general understanding is that they essentially mimic an existing lens. And there are still problems here and there. We will see if the problems get worse as Canon moved to RF mount.