I really cannot wait for this figure!!! I love everything about this guy (and the newly announced B/D version)....
I would love for Hot Toys to make a Robocain Figure. I think he would make for a quite complex and amazing piece and would sell very well.
More then likely the main reason HT haven't produced a Cain figure is the engineering on the model is too complex and cost prohibitive. Can't think of any other reason they haven't done it yet. Don't forget the original Cain puppet was designed to be the most complex one ever exactly for the reason that toy manufacturers couldn't reproduce it. If you want a cain your only option is the chronicle collectibles 1/4 scale model which is being released later this year.