-More Detailed Tiles: You see, currently the number of objects a given tile can have is extremely limited because of the memory requirements of having them on the map. In a one tile system they would only be generated when one views the city view screen. This means we can use tons more objects when making a tile without memory constraints. This is very important for modders and users that want to play on large maps. There are several features that could be implemented if we only had more memory to work with.
More detailed art always comes at a trade-off in memory. Just because it isn't shown on the screen all the time also doesn't mean it isn't in memory. In order to have a quick transition between map and cities you'll either have to use more memory or the quality will suffer.
-Better Game Performance: As said above, the memory requirements would be greatly reduced. That means more of other things can be put on the map, like monsters that have more than one unit in the army. People with slower computers will be able to play larger maps. Currently the endgame is sluggish for almost everyone. The large cites are the greatest contributor.
Do you like waits for loading screens? Having another engine and pop up box for more detailed city art means longer loading times. This is not better game performance. Now if you're just making a crude Civilization style city screen it can be relatively quick... and gamey.
-Better Scale: Scale, as has been hashed through many a times by me, is all about measurements matching up. A single tile is hundreds of square miles. It is hard to justify a city taking up more than one tile. Sure, some things like rivers and cities are representationally larger on this kind of map, but the don't take up 50% of the map. If we want choke points, there are better ways to make them. Use magic to create mountainous walls, give units an ZoC on the main map to slow enemies, allow massive walls to be constructed in strategic areas. There are many solutions that work within the current scale of the game. City snaking is a gamy solution to strategic play.
This is ridiculously subjective to what you think the scale of the game is. I personally never viewed the map as a "planet map" so it wasn't an issue. Also, one person walking a distance is far different from trying to lead a group together. Again though, highly subjective and variable.
-Sieges: Sieges are not a design option, as stated by the devs, in the current system because of several constraints. It would be easier to implement alongside a one tile system. It creates a view screen that could show the player a siege without rendering it on the strategic map. This is not my area of expertise, but generally Hf is right about these things.
Again subjective. If you can code it on a single tile, you can code it on multiple tiles. Before you can say one is better for sieges than the other, you have to actually have a plan on how sieges would work. Otherwise it becomes a war of hypotheticals.
-People shown in the tiles: This is a kickback to the good old days when we had a bustling city with lots of little people walking about. I really want this back. It was removed as an option due to memory constraints. Never Forget.
I haven't forgotten and it was nice. It was also only available when zoomed in to max. Anyways see before, all memory discussions at this point are a matter of hypotheticals. If you increase the graphics demand on memory, you'll only make it worse.
-Whole new dimension of effect possibilities for this screen: Magic can be seen affecting cities, Sieges can be viewed here from season to season, destructible buildings and walls: Once again, we are not understanding each other. I mean they can create magical graphic effects for the city. A city could be frozen over by a water spell. That spell would visibly show up on the city, freezing the people and buildings. This cannot be done until we have a city view screen. There are dozens of things that could be done on a city view screen that cannot be done otherwise.
Already possible, and in my opinion breaks immersion less when you don't have to cut to a cut scene or the miniscule effects on a single tile city to do it. Surrounding my uniquely shaped city with a fire wall is a lot more realistic and interesting than a city cut scene fire wall or a single tile city.
This whole thing is still using a cannon ball (Complete city revamp) to swat a fly (snaking). First consider why do people make snaked cities? What is the root cause? Can it be addressed without blowing up cities as they existed in beta 2? One could address resource distribution on the map. How mountains and canyons cut off buildable areas, etc. Revamping the entire city mechanic is an incredibly drastic change to address so specific a problem.