My only apprehension is that they're a relatively expensive, heavy solution to a non-problem (wet braking with alloy rims).
Granted, poor wet braking is an issue with carbon rims, but as has been pointed out, pros will not tolerate the d-brake hit in weight and drag, and recreational riders wouldn't be on carbon rims anyway. As for the dentists on Colnagos and carbon rims -- they'll do whatever the pros do.
I wouldn't say it'll never happen --
http://www.volagi.com/bikes -- but it's the sort of thing that will be a very small, conversation-starter-at-the-coffee-shop type of product. Guys with bamboo bikes with disc brakes get all the chicks.