I think one of the problems with dark sun as a D&D setting is that magic should be rarer than it was. Defilers were scarey but rarer, and preservers were lumped in with all of them. Psionics, on the other hand, while it was integral to the setting, never played the full role that it was played up to, so it isn't as integral either.
the real grit (sand, grit, haha... yeah bad pun) of the setting comes from it's attitudes about magic - attitudes mirrored in IH almost perfectly.
Maybe some kind of lessened but "safe" psionics variant would fit into the setting better. hmm.. the templars have never really been as focused on magic as they are on the administrative details of a city-state.
I'm not adverse to changing the setting basics around a bit to suit IH better either, honestly, since I think the flavor would be really easy to maintain.
I'll ponder more...