Doesn't it all boil down to texture, recoverablility, and the hazard material's relationship to naturally occuring features, as TEP has stated above?
We have seen the advent of "environmental zone" hazards in the last 30 years. Green staked areas where one is not allowed to enter to recover a ball. It might as well be a water hazard since texture of the material that the ball lies within is irrelavant and the recovery shot can't be attempted. Then there is the lava flow variety. I never played at a course like that, but I assume that if your ball lies in the craggy and rough lava, and you are goofy or a gambler, you might elect to not ground your club and hit the ball, chancing ruining your blade on the sharp material. Not a very viable option IMHO. Then there are the darn unenterable flower beds that play like the enviro green staked hazards. All these are not compatible with recovery and are undesirable in my opinion.
Obviously, the rough grass area (perhaps with a modest level of minimum maintenance of 4-6" and sprayed for broadleaf infestation) in hollows like a grass bunker, or on convex mounds or hummocks offer the best potentially recoverable and naturally occuring material of a texture where the club can be utilized to attempt a shot.
I have always been curious about Shivas (Dave Schmidt's) ideas on rough strips meandering within fairways and crossing them in diagonals and such, challenging ball placement or extracting a half shot or so penalty on the recovery. While they wouldn't necessarily pass the naturally occuring test or traditional golf course appearance, they sound interesting and possibly worthy of a try by some specifically or conducively laid out course with wide fairways and few bunkers.
Waste areas also present the more logical areas to try different materials of a texture that allows an attempt at recovery, without ruining a golf club. There are those experiments with the coal slag and by products of industry of various regions. They have the pine needles which are sort of a hazard texture with unique playing characteristics for hitting shots from them. They have crushed marble and other stone, and some artificial ground materials. I suppose one could spread wood chips or sawdust, or ground corn husks or corn or grain. All of which is silly stuff, but at least presents the possiblility of a recovery blow being struck at the ball that landed in such a hazard zone.
I don't like rock walls, stone fences, boulder fields, hard scrabble fields and anything of a man made permanent barrier including RR ties, as a personal point of distaste. Using old structure foundations and basements like Hurdzan's use of some old farm building at Devils Paintbrush or Pulpit or whatever... is undesirable in my own personal bag of preferences.
So to conclude, I can't think of anything more valid than the above discussed "rough strips, hollows or mounds" or pine needle areas, or sandy wastes or wastes of some natural or indigenous to regional industrial by-product material as proper texture for a hazard area.
Oh yeah, trees... deciduous preferred or coniferous with bases trimmed up at least 4-5ft from ground level offering some chance to punch out from beneath...
