Not in the Outlands, presumably, since that Plane went the way of the Dodo... maybe the Astral Sea?
So if Sigil is going to be in 4E, where is it located?
Perhaps.... they just won't say. Its Sigil - you can only get to it by portal so nobody knows exactly where it is. After all, we've only presumed for all these years that its at the top of the spire. The evidence is entirely circumstantial
My bet however is that its "at the top of an infinitely tall spire of rock on some strange island in the Astral sea that represents True Neutrality and a safe haven even from the Gods." That seems to be the style of the cut and paste of old editions that 4e will be.
I think the Outlands still implicitly exists, but their "no symmetry!" mandate means that it's not the center of the Astral Sea (of course, the outer planes never had a center, as the Center of All rule shows). I don't think we'll see any mention of magic-deadening rings or 16 portal-towns arranged in a circle, and any divine realms that were once in the Outlands will probably be astral dominions in their own right.
I lean toward Armoury's idea, that Sigil will be located atop a tall spire (they won't use the word "infinite") in the Astral Sea. I don't think they'll use the word "neutrality," though - alignments seem to be too old-school for the current fashion.
I wouldn't call it old school. Basic 1st edition D&D had all the same alignments we have today.
I don't mind having some creatures that are strongly aligned (exemplars come to mind), but in general I have found the alignment system to hinder roleplaying, rather than being an aid to roleplaying.
(Not that 4e is really about roleplaying, heh.)
BoGr Guide to Missile Combat:
1) Equip a bow or crossbow.
2) Roll a natural 1 on d20.
3) ?????
4) Profit!
How do you figure? If your character does not act within his alignment, his alignment changes. It says so right in the 1st D&D Basic book. Alignment is a tool not a constraint.
Alignment in the hands of DMs and Players who know it's a tool - is a tool. In the hands of DMs and Players who use it to browbeat each other across the screens... not so much. It really depends on the habits at the gaming table.
Because mortal beings (and some more complex player characters) seem to be multi-aligned. In some situations, they behave in a more "good" way, but in a different set of circumstances, they behave in a more "evil" way, depending on culture and individual psychology. Same for lawful and chaotic. But they're not really 'True Neutral'-aligned.
BoGr Guide to Missile Combat:
1) Equip a bow or crossbow.
2) Roll a natural 1 on d20.
3) ?????
4) Profit!
I always figured that True Neutral was the absence of strong leanings towards any of the extremes, but that doesn't quite seem to be what you are getting at. Could you give an example maybe?
BAH! What the hell do WOTC know? Its located exactly where it always was, atop an infinitely tall spire in the centre of the outlands, the plane of total neutrality! Either that or its now deep within the bowels of some WOTC executive.
Didn't you get the memo? 3rd edition is old school now.
I think they're still trying to decide that, and chances are it may be the same "place" or the more ambiguous "place that isn't a place" in an unknown location in the multiverse, which Sigil also was, since no one really had any solid proof it was on top of the spire in the first place, other than seeing something there that was sort of shaped like Sigil.
My pessimism is telling me it's on the prime, or whatever it's called now. Just because that is the worst thing I can think of.