(I supposed there are potential (minor?) spoilers here for folks who, for example, haven't done any of the Hildibrand quests. Just a heads up.)
(Also, this site has some decent 1.0 maps if you're interested/nostalgic:
http://ffxivmaps.com/old.html)
It's nice that we're finally heading back out to Coerthas Western Highlands, but what about some of the other areas from 1.0 that we can no longer enter? (Though, I'm sad we may never have Gargoyle Crossing again, since I imagine we will bridge Coerthas Western Highlands and Coerthas Central Highlands with a tunnel through/past Snowcloak instead of the previous, well, bridge. Or fly there from the Sea of Clouds.)
Nanawa Mines
The connection between Central Thanalan and Northern Thanalan changed drastically in 2.0. What happened to Nanawa Mines? Is Nanawa Mines what the mine/train tracks lead into? Or is Nanawa Mines completely caved in, and the pass leading from Central Thanalan to Northern Thanalan is all that Ul'dah dug up of Nanawa Mines in order to pass through? The map seems to refer to the entire construction area as "Nanawa Mines", rather than indicating any entrance (though the zone line is quite close, and in 1.0 Bluefog was just a bit north of where Nanawa Mines would have been).
Copperbell Mines
But, wait, you already can access this area... right? Don't open the spoiler tag unless you have finished the main scenario quest up to 2.55's story!
At the end of the MSQ, it shows the Sil'dih Aqueducts. Copperbell Mines in 1.0 was actually adjacent to the Sil'dih Aqueducts, an unusable entrance to them being included in the area. Also, the Copperbell Mines were much larger in 1.0. We are only able to access part of them. Will we ever be able to explore the Sil'dih Aqueducts, or the missing sections of Copperbell Mines? The former being much more interesting, of course. I was actually thinking about how in FFXI some of the cities had underground areas accessible directly from the city (leading into a dungeon and/or making a passageway to a distant area), and was wondering if we'd ever see something similar in FFXIV, and then the MSQ shows us the Sil'dih Aqueducts under Ul'dah! I've been wondering for a while if we will ever visit the ruins of Sil'dih...
Mun-Tuy Cellars
How did the Cellars move from North Shroud in 1.0 to being the bridge between East Shroud and South Shroud in 2.0!? I understand some areas being moved around slightly (Snakemolt being east of where it was originally... it's not too crazy to think the people would just use names they were familiar with and apply them to "new" areas instead of making up new names, after the landscape changed), but an entire underground section moved clear across the forest? Mun-Tuy Cellars clearing bridging two zones does lend some weight that Nanawa Mines will never be used as more than a zone line connection, though.

Originally Posted by
Fernehalwes
Greetings Hiruke!
The fermenting of Mun-Tuy beans into sauces, tonics, pastes, and even the tasty brew that helps Wood Wailers wind down after a long day of wailing is a task that requires strict temperature and humidity control. In an age devoid of heating/cooling systems, the best place to achieve perfect temperatures/humidity was in caves (no matter how hot/cold it is outside, a cave's interior usually remains unchanged). It also helps that on the walls of certain caves found only in the Twelveswood grows a special type of yeast that helps transform the Mun-Tuy juice into something more...exciting. When the Calamity wreaked its havoc on the Twelveswood, many of the caves used for Mun-Tuy processing were either buried under rubble, or new openings were created, changing the internal environment and making them no longer suitable for the task at hand. This is pretty much what happened with the pre-Calamity cellars. However, Gridania is a thirsty city-state, and the Mun-Tuy brewers were not ready to let their craft fade into oblivion, so they searched long and hard for a new series of caves that met the conditions of their old cellars...and finally found some on the border of the new East and South Shrouds--the location of the new cellars.
I know that doesn't answer all of your questions, but hope it sheds some light on one.
Taking another look at the maps, the (new) Mun-Tuy Cellars are HUGE, because there's is a LONG distance between East Shroud and South Shroud according to the 1.0 layout. Now I definitely wonder if we'll ever explore this area (though I guess there isn't much need to).
Some other areas I missed in the initial post, now added to the OP:
Cassiopeia Hollow
A dungeon area near 1.0's Camp Bloodshore, presumably this would be somewhere near Costa del Sol now, but it's not really hinted at anywhere. I would imagine there would be little interest in reviving this area as Sastasha already covers what it might offer thematically? Still would be interesting to know what happened to it.
Shposhae
A dungeon area near 1.0's Moraby Bay aetherial gate, presumably this would be around where "Moraby Bay" (the bay itself rather than the drydocks) is marked on the map, but it's not really hinted at anywhere. I would imagine there would be little interest in reviving this area as Sastasha already covers what it might offer thematically? Still would be interesting to know what happened to it.
Coerthas Central Lowlands
Probably the most perplexing inaccessible 1.0 area is the Coerthas Central Lowlands. In 1.0, Mor Dhona zoned north into Coerthas Central Lowlands. Now when we zone north from Mor Dhona, it skips the Coerthas Central Lowlands entirely and goes straight to Coerthas Central Highlands. The northern part of Mor Dhona and more or less the entirety of Coerthas Central Highlands are mostly similar to their 1.0 counterparts, so skipping this entire area is quite odd.
It's also a little odd that North Shroud used to zone into Coerthas Eastern Lowlands, but now somehow winds all the way up into Coerthas Central Highlands.
Coerthas Eastern Lowlands
Griffin Crossing is currently down for repairs (despite seeming not that bad off when used as the site of the first battle with Gilgamesh), so it's understandable why you can no longer zone in to there from Coerthas Central Highlands. It's kind of odd that the connection between North Shroud and Coerthas Eastern Lowlands has been replaced with one between North Shroud and Coerthas Central Highlands. Is that ever explained anywhere?
I imagine the poor Ishgardians stuck here around Owl's Nest could use some visitors!
Coerthas Eastern Highlands
Sure, we're now going to the west, but how about the east? This is probably one of the most understandable areas to get blocked off, since the only way in was a tunnel from Coerthas Central Highlands. Surely, similar to attempting to repair Griffin Crossing, there is some effort to reopen the tunnel here as well?
Mor Dhona (southern section?)
Mor Dhona is probably one of the more oddly reworked areas in 2.0. Singing Shards now to the east of Revenant's Toll instead of southeast of Silvertear Lake. Somehow, Silvertear Lake is called Silvertear Falls on the map!? How does that even work? Northern Thanalan used to zone into the southern part of Mor Dhona, but now tracks around to the northern part of Mor Dhona instead.
Basically, you can no longer visit the southern end of Silvertear Lake. This is probably one of the most "losable" areas of the game, though it would be interesting if Revenant's Toll eventually expanded into a full-blown city and they decided to explore the rest of Mor Dhona, uncovering the ruins of (well, I assume it's ruined?) Castrum Novum from 1.0 and whatever happened to Camp Brittlebark, etc.
West Shroud
I believe it was said this part of the forest was basically completely destroyed. You can see what's in its place over the rise west of Spriggan's Dig in Central Shroud, and some speculate that you actually bypass this area when moving between Central Shroud and North Shroud. Even if nothing (natural?) lives there, it would be interesting to explore a more "destroyed" zone at some point in the future.
Summary
For the most part, I think the team did a fantastic job reimagining all of the areas. If you compare the old 1.0 maps to the new 2.0 maps, you can see that more often than not, things are around where they ought to be, except the zones have a much better design overall.
However, from a lore perspective, missing a lot of the zones called out in bold above... irks me... Especially Coerthas Central Lowlands. Seriously, what happened to Coerthas Central Lowlands!?
Edit: Added Nanawa Mines and Mun-Tuy Cellars (and ninja'd in Fern's response).
Edit 2: Added Cassiopeia Hollow and Shposhae.
Edit 3: Added Copperbell Mines.