I believe we are very slowly approaching a point where CCRs finally, in their multi-century-long development, can become truly safe and mainstream. We're definitely not there yet, but we will see it in our lifetimes as sensor tech gets better. Perhaps we'll even see future generations of CCRs replace OC diving entirely.
I don't know if I buy any of that "mainstreaming of the CCR" business or its potential to ever replace open circuit. I had already been assured of the same thing, back in the mid-1990s; though I have enjoyed access to them on occasion -- don't get me wrong -- but I certainly believe that they will remain a niche market within a further niche market.
They've been around for decades, yes, and the sensor technology has greatly improved, yes; but the upkeep is still several times the cost of open circuit; and rebreathers also carry with them, all of the spontaneity, associated with a space shot.
I went diving the other day, just on the spur of the moment, taking along a regulator that I had recently rebuilt, which dated from some time within the Nixon administration, with maybe twelve or so parts to its unbalanced first stage and a like number in its second -- about a kilo of steel and chromed brass, which typically lives in a small catch bag, behind the bench seat of my Tacoma.
At that beach in Carmel, were two divers sporting rebreathers, who busied themselves with their laminated pre-check lists on a truck tailgate, by the side of HWY-1; and they were still there, doing much the same thing, after I returned from a sixty minute dive, when they apparently had just called theirs, for whatever reason . . .