Trying to be all things to all contenders?
Wolram, I really hope we can avoid starting a flame war here since you are asking us to comment on matters about which some people seem to feel very strongly. I'll try to give what I think is an even handed assessment which is equally unfair to all points of view currently held by a few dozen or more researchers, and I hope this will satisfy you.
If you don't know the lingo it's easy to be fooled into thinking that something known as "Chaplygin gas" is known to actually exist in the sense that a gas called helium is known to exist (and even has technological applications in the advertising industry, e.g. the Goodyear blimp), but that is not at all the case. The weasel word "exotic" in "exotic equation of state" is your clue that someone basically tried to invent an equation of state (an equation relating density and pressure) which would lead to some kind of heuristic model which might solve some observations currently lacking well established theoretical explanations, if only such stuff actually existed. Fair enough, since when you don't have a clue you start by playing around, but the point is that models of so-called "traversable wormholes" held open by so-called "exotic matter" are at present sheer fantasy. The difference between scientific fanasies and talking dragons is that sometimes scientific fantasies eventually turn out to resemble actual phenomena in Nature. More often-- much more often--- they do not.
As to "why everyone seems to want wormholes": well, fundamental theoretical physics has been kinda stuck for many decades; there are well understood mysteries but little progress toward devising experiments which can decide between competing theories or quasi-theories. In consquence of lack of "reality checks", theoretical physicists have gone rather wild in the past few decades and have produced many highly imaginative speculations, which they can get away with (to some extent) because there is as yet no relevant experimental evidence ruling out any manner of wild speculation. Again, in the absence of experimental evidence, there's little for theorists to do in the area of fundamental physics other than speculate; some feel that too many theorists have chosen this route rather than a "sensible" alternative, making theories of challenging but nonfundamental physics.
To be fair, were someone someday to establish by experiment or observation irrefutable evidence of traversable wormholes or even just some kind of exotic matter, that would be big stuff; some even think that if only exotic matter existed, they could figure out how to do nifty things like physically travel to distant galaxies. That would be fun, no doubt about it, but the trouble is that, modulo pedantics about stuff like Casimir effect, at present there is no universally accepted theoretical rationale for why exotic matter "must exist" or universally accepted evidence that such stuff does exist. That said, much of the current interest in exotic matter is driven by observations which may be indirect evidence for the existence of something vaguely resembling some of the hypothetical stuff which has been discussed under the umbrella term "exotic matter".
Now that I've offended everyone
I hope we can all let this rest! (Or move this thread to GD.)
