I suppose I should throw in my 3 cents.
For the most part what
@Jrr_ said sounds pretty cool, but since I'm already forgetting what he said and don't want to go back to that page, I'll just say some things about map/guild/whateverelsecomestomind ideas.
MAP:
I've seen some decent suggestions related to this. As far as keeping people interested, I agree that relatively huge map is necessary. I think biomes corresponding to latitude sounds nice, and also a large number of smaller dungeons scattered around the map that are blended into the landscape. Those two would help any RPers with immersion type stuff, and the large map would create a feeling of exploration.
On top of dungeons, there should be a large number of capture points which give tangible rewards, such as mines with ore veins at an increased respawn rate, temples that give minor exp boosts, castles that... do something, resource points that let you gather specific resources for item/guild upgrades, and mage towers that can act as warp points. These should only be fully accessible to the guilds that have currently captured them, but maybe a system where allied guilds that assisted in capturing the point but did not receive the final capture could still receive some smaller reward. That brings us to the next point:
GUILDS:
I like the general idea of a revised township, as well as what I vaguely remember being laid out in the first post. Basically, when a guild is first formed, you cannot claim land, but receive some sort of minor advantage in a small area within your guild's territory. In this zone, other players can still break/place blocks, it's just meant to give the defender bonus.
At a certain point and with x number of coins, you can purchase a GUILD HALL. This is a protected chunk which you are able to build in without non-members being able interact with it. Mayor's should be able to give out perms for who can place/break within this area. The other big part is that must have an entrance above ground, although it doesn't necessarily need to be accessible.
As guilds grow larger they can claim more chunks around their guild hall, as well as outposts which are protected, but this would be late game and require specific resources from the resource capture points which I talked about before.
ECONOMY:
Yeah, trade district stuff is good. Souls vs. gold I could go either way on, both have advantages. As far as combating inflation (which we have a lot of) gold would be better just because there's only a limited amount accessible to people through mining. Then you'd probably get some through quests and voting. But that reminds me:
QUESTS:
Quests are good. Have an NPC or two outside of a dungeon which tells you to kill a certain number of a specific mob, or get inside and retrieve an item. Other quests at trade market might be to gather a certain number of an item such as coal or redstone or lapis that might not otherwise have massive amounts of use for their lack of rarity. Then you would obviously have the NPC's in a "war-room" that tells you to kill X players or to capture a specific type of capture point (mine, castle, lumber mill, who knows) which would be the same for all players daily. Rewards depend on quests, but usually a good amount of exp and a small amount of coin.
PVP/RAIDING:
With the system I just proposed, most PvP would be around the capture points which are the focus of that day's daily capture quest. With the new guild system, raiding would not be as common, but guild wars (not a reference to guild wars game) could be in where each chunk acts as a capture point which, when captured, gives a reward through gold/resource to the capturer and must be repaired by the original guild through some gold/resource.
On top of this, we need a cool arena system. Ranks based on in-arena performance, where you can only have a specific matchup once per day in an attempt to prevent grinding, and points are given to rank based on W/L ratio of who they beat.
SPAWN:
So basically, you guys remember Solitude from Skyrim? How it's a peninsula and you have to walk through the whole city from the palace to entrance in order to leave? Make it like that, so that people walk through the trade district and past noble plots in order to leave, then you get to the hero gates. Spawn would be at the palace in this scenario. Also have a single common area which has the most expensive shops and some mini-games and a view of the arena (if it were to be in the main world and not instanced).
CHAT:
Just remembered this. To prevent clutter, make it similar to how WoW does it (just the example I can think of) where you have a region chat, a yell, a standard local, and a world-wide guild chat. This gives further incentive to congregate in spawn if you are looking for an item or just want to hang out. I'm not sure what the LFGuild would be, because I see advantages for it being either world-wide and local.
That's all I can really think of ATM. Please forgive spelling and lack of snazzy colors, I'm doing this on mobile.
TL;DR I think what some people suggested is pretty cool, but focus on a variety of activities.