Basically you are talking about the Presentation Arc.
You can find some more infos about it in this thread:
http://www.bay12games.com/forum/index.php?topic=21099.0
Here's the most important part:
1 - Yes, graphics support for items, terrain and so on, and it's not possible at the moment to attain a separation from the text for anything aside from creatures.
If you think about it, items have more current graphical diversity than can be handled by the item tokens. For example, chunks of hematite and mudstone are both of item type STONE, but use different tiles, since one is a metal ore. And building tokens don't even exist yet. The current graphics were easier since all creature definitions are in the raws, and the profession tokens were necessary for entity definitions. (just my outsider's guess, of course)
Man, I hadn't thought til now about dwarves in the next version having distinctive characteristics (hair color, etc.) that cannot possibly be expressed via tileset. You would need some kind of palette-swapping at the very least. Considering the level of detail the game is already reaching, I can understand Toady's disinterest in graphics -- it's such a gigantic can of worms.
On the other hand, maybe palette swapping wouldn't be that terribly difficult -- say you create a tile with areas of exposed skin colored pure green, then use a tag in the creature graphics definition that would tell the game to substitute green with the color of one of that creature's features. It could look something like [COLOR:0:255:0:SKIN], [COLOR:0:0:255:BEARD]. Okay, this is a really dumb line of speculation, I'll stop now.
Oh god you could even include a brightness percentage in the tag, so by using two shades of blue in the beard you could ensure the palette-swapped beard would have slightly darker lines to indicate texture, regardless of whether it was red or blond. Something like:
[COLOR:0:0:255:BEARD:100] (dwarf's beard color, at full brightness)
[COLOR:0:0:254:BEARD:80] (dwarf's beard color at 80% brightness, for darker sections)
Stopping for real now, but I think I just turned into a graphics whore.