Tl;Dr Guild activity ressources and more and better guild Shop Items.

Add (more) ressources gained solely by doing guild activities and add guild shop items only purchasable with those ressources. The Guild Shop items must be limited time, which forces the guilds to gather more of them. Elephants and Guild Ship are cool and all, but it they are one time activities.  These Guild shop items should be powerful enough to warrant the time investment into doing it. Ridiculous things such as birthday cakes, +200 mastery, pure blackstones, Guild wide buffs for a limited time.

PvP missions for RBF, Open world, Guild wars, Nodewars, Siege wars.

Adding Additional ressource gain from owning  a node. Some may be done by individual players.

Suggestions for missions:

Win a Guild war in a limited time with a certain amount of kills. Win a nodewar. Defend a node. Reach X amount of points in RBF by killing non guild members

Blackstone extraction sites in the black desert, which must be defende from other players(guilds can join either attacking side or defending side)

Guild mission wars between valencia and calpheon and only kills in a certain area count ( for example the desert). Both sides should have multiple spawn points

Lifeskill missions: Add missions for other gathering items such as meat, blood, saps, fishes etc, Hunting bosses, Sea monster bosses,

Guild Bartering. Bring an Item to somone. Every guild can only transport 1 item at the time. However you can steal from other guilds. This must be done more than once.

PvE missions: Kill X amount of mobs, (instanced, world, field, summoned) Bosses, Find a certain amount of items, 

Blackstone extraction sites in the black desert, which must be defende from other mobs, Gain points by repairing or killing mobs. Structures could be added

Most importantly: Allow multiple guilds to accept the same mission and compete with each other to have more distribution. Higher contribution gives higher rewards. Only allow a lowish amount of guild missions everyday. It shouldn't be possible for everyone to get something. Scarcity is the most important factor for competition. This could further be increased by adding a high price to accepting guild mission, which really forces a guild to do well. These can of course be tiered by sizes of guilds.

Shop ideas: Consumables (elixirs, food, potions, cannonballs, traps, magic carrots), , Limited time gear upgrades to gear similar to the Cups or Garmoth, LImited time gear upgrades, Pure Blackstones (high prices), very strong guild wide buffs for a limited time( 50 ap, 100 dr, 50% lifeskill exp, 100~200 mastery, ), Improved Boss summon scrolls, Upgrades to the Guild houses ( buying villa scrolls, NPC buffs for energy, A priest to roll gold) 

I'd add the need of improving existing activites such as guild bosses. Some have been reworked but there are some others that still have outdated rewards such as Muskan, Griffon and Offin.

Yes, I tried to include it by writing "improved boss scrolls". Many of them are simply outdated in the incentive/reward aspect. A possibility could be to allow the dropping of the ressources required to craft more consumables or purchase consumables from the improved guild shop.