I see alot of the aspects of ED in 4e, the multiple defenses to test
against, the 4e powers are similar in ways to ED.
I have seen Earthdawn 3.5 d20 and is somewhat of a bastardisation, it
really doesn't fit. It might be possible with 4e.
ED works on a step system, the numbers rolled are totalled for the
result. No +'s or -'s after the roll. It has simple modifiers on a
table of dice, which are kept deliberately simple.
ED is a roleplaying game, I've had entire sessions with no dice roles.
DnD becomes ever more like the miniatures version. (which I think they
prefer to push, looking at the mass profits Games Workshop made from
it's model range). I try to discourage out and out combat as a
solution in ED, as there are a number of beasts that could easily kill
off lower level parties. DnD 4e is extremely balanced and so will
always give an appropriate combat challenge if the setup rules are
applied.