Tom, Ipe is and has been grown commercially and sustainably in areas that are not ex-rain forest. One other factor is that ipe is so dense that it practically does not burn. Those special fasteners it requires are the same stainless steel screws or nails that most decks are now built with, other than the pressure treated wood decks.
It does have a high hardness and silicon content which is tough on tools and tooling. You have to use sharp saws and drills for best results. Personally, I would prefer these factors to the soft and stainable redwood. And I am sure that if you do a search at www.woodweb.com, you will easily find posts at the sawing and drying and the WoodnetWork forums confirming this. Look for the posts by Gene Wengert, the retired forestry professor from Wisconsin, and now a consultant to several facets of the industry. Then check the ASTM E-84 (Surface Burning Characteristics) values for ipe as well as the fire insurance code classes.
If I were in the redwood business, I'd be closely watching this too. The wood now does come from sustainable sources and has twice the mechanical properties of redwood. As it has become more available, the prices have come down and they are at or less than those of redwood in many parts of the country. The prices were a result of too many people getting a mark-up in the supply chain. I have been able to buy all I want from stocking sources for very reasonable prices.