Probably no one has done it because it's most likely not necessary and increases costs. I don't know enough about trex substructure to comment on the advantages over traditional framing.

That's kind of what we've been wondering. It seems like they've been pushing the Trex products (framing, rain escape, aluminum railings) on us, and as a result, the cost of the project is going up and up. The rain system (to keep the patio below the deck dry) costs more per L.F. than the ipe! Plus, if that system keeps the frame from getting wet in the first place, why do I need the steel? Hmmm!!!

did you guys ever do this project with ipe / trex elevations frame substructure ? i'm considering it also.. Thanks

Ipe is heavy: basic specific gravity (oven dry weight/green volume) 0.85 to 0.97, air dry density 66 to 75 pounds per cubic foot. A 3/4" thick finish material weights approx.4.5 pounds per square foot. However, there is no need for steel superstructure. Conventional beck building works. Specifics: My ipe deck is 12ft x 90 ft and it rests on conventional pressure treated lumber posts that are clad in ipe board just for look. The deck is attached to the side of the house via bolts just like any other decks. The deck is rock solid after 14 years already.