The RZ67 was designed to replace the RB from the get go. No doubt whatsoever. It was only later that they finally realized people were going to keep buying the RB (for whatever reasons) and decided to keep making them. I am sure they would have preferred to not bother, probably. But the money was too good, I'd guess.
What functionality was lost? None that I can think of. Everything was/is a gain - which is why it was designed as a replacement. the RZ is a superb system, and especially these days with the crazy cheap prices, no reason not to choose it over the RB. RZ lenses are actually cheaper in many cases than RB lenses (more of them available, the APOs for example).
Originally Posted by MattKing