This article doesn't mention type of diving (ie-deep, wreck, higher risk, etc) behaviors among rebreather diver deaths. And it doesn't mention where, when, and how the divers, that were using rebreathers, died.
I don't know if there have been any significant changes in technology, but one would imagine that the safety has gotten much better and will continue to improve, just like all other machines. rebreathers fascinate me to no end. I would love to be able to spend hours in the deep, but I'm not sure if I am ready for rebreathers.