Geez, for the love of God! Everyone is getting so worked up over a setting that they haven't even seen yet! All we've seen are some pictures of the concept art, and nothing else. Perhaps the "train" is confined to a particular advanced magic kingdom. The setting may rock, or it may suck. It's far to early to judge yet!
As far as realism goes, GET A LIFE! It always annoys me how some historical inclined players get so worked up over what would and wouldn't be possible with "medieval technology". D&D never was meant to simulate medieval life. Gary Gygax even wrote it himself in the introduction of the original DMG (or maybe PHB, I forget). Anyway, I could point out hundreds of reasons why Forgotten Realms, Greyhawk, or Dragonlance aren't "realistic", but why bother? They're meant to be fantasy. This is just as bad as these physics nerds that have to ruin every science fiction movie by pointing out all the physics flaws in it.
The irony of every thing is that I remember when the search was announced last year, everyone was bemoaning the fact that there were already to many "Tolkien-inspired Euro-fantasy settings." Many posters wanted something different and unique. Well, it looks from what I've seen, that the setting will, indeed, be different and unique. Now everyone is griping that the setting is "too different", or it deviates to much from the standard "medieval" setting.
Personally "techno-magic" sounds kind of cool to me, but really it's to early to tell if Eberron will be cool or not. As a fan of the Final Fantasy games, the whole idea of magic and technology sounds neat. I suppose it is all really a matter of taste. Some people like grim, gritty, and tragic fantasy. I do not. I enjoy heroic high fantasy, with larger than life heroes. I've heard praise for Midnight, but after tooking a look at it I didn't like the setting at all. (Although I admit that it was well written.) I though that it was too dark, and had too much of "Alas, evil rules the world. You are a legendary, but ultimately doomed hero. You can't win." Some people love the setting. IT'S JUST A MATTER OF PERSONAL TASTE! Is there anything wrong with enjoying high fantasy and magical technology? Then why is everyone complaining!?