I have done my share of zero/low visibility diving, and I can think of a few things that may limit a blind diver. One is current. I dive mostly in rivers right now, and a blind diver, even with two sighted DiveHeart Divers, could have problems in a river current, or in an ocean area with a fairly high current. This could cause problems in cave diving/wreck diving too, as in current there are back eddies, and places where a sighted diver becomes disoriented due to conflicting currents.
The other is cold water. Any water where the divers need to wear gloves because of cold, may inhibit a blind diver. Why? Well, think of it, as a blind diver probably uses touch a lot more than a sighted diver. This is not only for signaling, but also for contact with a line, with the bottom, etc.
Depth may be a factor, in that with increasing depth there is more decompression problems. But this may be alleviated in the future with the potential for “talking” computers (yes, this is a possibility). However, the depth probably should be limited by the potential for nitrogen narcosis, which can cause both sighted and blind divers problems.
SeaRat