In Medieval times, Guilds were groups or societies of people that shared the same profession. These would work together to get the highest possible profit, and to protect the economy. In Guild Wars we see this too, although Guilds are not really profession based but more what part of the game interests the players most. But these specialized Guilds are mostly seen in PvP as for example HA Guilds and GvG Guilds. PvE has 'title grinding guilds' and 'elite mission guilds' but I think everyone can agree with me that specialization in PvE guilds isn't as big as those in PvP.
So, this is where my first idea comes in. I suggest in GW2 Anet implies an extra option in guild creating, namely the 'Guild Type Option'. This option would allow Guild creators to pick between a list of types. This is the list that I came up with:
1. Corsair Guilds.
2. Mercenary Guilds.
3. Imperial Guilds.
4. Bandit Guilds.
5. Assassin Guilds.
So, this is all nice of course, but does this make Guilds any different from eachother? No, it doesn't, but that's where my second idea jumps in.
Although we have Dungeons and Elite Missions, Guilds in PvE don't have something as GvG; where a guild is forced to play together, and where the real team feeling exists. So what I came up with was the following; Guild Missions. Just as GvG these missions would start in the Guild Hall, but these wouldn't be PvP, but PvE. This is also where the difference between the Guild Types actually exists:
Corsair Guilds would for example get a mission in which they land a ship on a coast, than the ship would be attacked by Krytan Guards. The Guild has to defend the ship, after which it has to escort a group of goods carrying NPC's to a nearby corsair market. The reward for the Guild, next to the loot gained from dead guards, would be a certain amount of goods depending on how many NPC's they kept alive.
That's the idea. An Assassin Guild would be infiltrating in a Undead Camp of Palawa Joko, after which they slay the Mordant Crescent leader of the camp. Their reward would be an armor piece for each of the participating Guild members.
Mercenary's would be hired to kill a group of rebel's, or to escort an important person, after which their reward would be cash money.
Etc etc, Imperial Guilds would clear a main road of bandits with their reward being weapons and Bandit Guilds would get all sorts of loot depending on their mission.
These missions would be in teams of 12 or 15 (seems to be the most balanced), and would be in an instanced area.