For reasons of compatibility and lore, Kvatch will not be affected in any way. The Imperial City will also remain untouched, for obvious reasons.
The plan breaks down as such for each city:
Anvil: Will be transformed into as close a representation as I can make of the concept art included on the Oblivion Collector's Edition DVD. Due to content distribution rules, I cannot link to it, so if you don't know what this layout looks like, just trust that it's pretty cool and will justify Anvil keeping its high city walls. Content from the Anvil Bay Expansion may end up being removed if there's no need for it with the new layout. Otherwise it will be kept to fill in any needed spaces.
http://img685.imageshack.us/img685/7948/bravilrebornoverhead.jpg: The castle area retains its walls, the rest of the city loses them entirely and relies instead on their island nature to be used as a defense. A dock has been added to the south side of the city, along with a small farm to at least make it appear as though they can feed themselves. Every 5th day of the month, a ship will show up at the dock, to simulate ongoing trade. You can also see that in the SW corner next to the cathedral that the book store for Lost Spires fit in nicely and that patch is untouched. Pretty much all compatibility for Bravil will be unaffected.
http://img693.imageshack.us/img693/9128/brumaeastgateoverhead.jpg: The city has been reorganized with the castle as the central feature, and the rest organized into districts. A lower class district along the north side, with the cathedral. The market district in the NE corner where all of the shops and guilds have been moved to. The upper class district on the SE side of the outer castle wall, where the Jerall View Inn now resides. And the middle class district along the SE wall of the city. The city walls surrounding all of this have been replaced with wooden palisades. Land space has been reserved for the two patches which place buildings in the city.
Cheydinhal: The castle will be moved to occupy a central position, with a similar reorganization of the commerce and lodging around that, and residential surrounding that. No work has been done on this yet as no suitable city wall replacements have been found.
Chorrol: The castle area will be repositioned into a more central spot, with the rest of the city being realigned around it. Giving some strong thought to eliminating the outer walls on this one entirely. But if not, I may go with resized stonewall meshes if something more appropriate doesn't come along. No work has happened on this yet.
http://img43.imageshack.us/img43/1396/leyawiinrebornoverhead.jpg: The existing layout for OC Leyawiin Reborn is being retained, though I may see if I can bring it http://www.elderscrolls.com/images/art/ob_concept/ob_concept03B.jpg Bethesda provided.
Skingrad: Undecided as of right now. The place is pretty tightly packed and more or less laid out nicely as it is. One of the few places that followed the concept art as-is. So it may not need to be bothered at all other than to get some slightly more appropriate walls.
I'm not ready to put out a WiP package just yet because I'd like to get Anvil included with it. I just wanted to show off what's been done so far. Bravil and Bruma look great, and performance in both cities has been boosted some as a bonus. Certainly wasn't expecting that, especially in Bruma since the palisades are much smaller than city wall pieces and therefore required MANY more of them to be placed.
I understand Phitt will soon be releasing resources which will contain walls that should be fitting for use in Cheydinhal. So if nothing else comes along there I'm content to wait for those. I'm wide open to suggestions and/or contributions for Chorrol and Skingrad though.
Also worth noting I will not be altering the layout or fortifications for New Sheoth as it has a valid lore based reason for needing ridiculous walls. Plus, Sheogorath's prerogative. Who am I to argue with the Mad God?
The open version of Bartholm will also remain untouched as I figure if J.Sera wants it changed he'll change it and I'll simply follow suit.
Do not ask for time estimates. I wouldn't be able to give you one even if I knew I had everything I needed.
Also, because there was a clear lack of use shown in the poll (sorry to the 9 of you who say otherwise) the open version of Bravil Blood&Mud will not be supported in this at all. There are techincal issues which make supporting the merge package more pain than its worth to maintain. Plus, with all of the additional clutter burden imposed by B&M, frame rates with it are unacceptable. Sorry, you'll just have to play that mod closed if you want it.