Perhaps some new classes for the next GW instalment, a new type of storyline, new type of world hub, the ability to play in offline mode (requiring no online accounts or internet connections whatsoever), a new map creator, more character variants, reworked sticker shop, a streamlined stickerbook etc.
New Classes - Plants
Melon - A new type of plant class that throws whole melons at enemies in an arc-firing pattern, headed by War Melon. Based on the Melon-Pelt from the original Plants Vs Zombies.
Shroom - The first plant class where mushrooms can now be controlled by players, headed by Battle Shroom. They are small, agile characters equipped with dual, scatter-type weapons, and they can call in their massive Giant Shroom Mechs to aid them in battle.
Apple - A new type of plant class where they specialize in suppressing their enemies. They are headed by war veteran, General Apple.
New Classes - Zombies
Robo-Soldier - Previously seen in GW2, the Robo-Soldiers get their chance to be in the spotlight, headed by their namesake leader, Robo-Soldier. They can punch their enemies up close, and can fire rockets at enemies from afar.
Dog - This new zombie class has the ability to burrow into the ground, move along, and then eat their enemies very sneakily, and their bites pack a punch at close range. They are headed by Zombie Dog.
Magician - A new zombie class headed by Zombie Magician. Their weapons work in a manner similar to the Rose class, where the projectiles coming from their wands can track down enemies. The magicians have the ability to the Sheepify their enemies, turning them into harmless sheep.
New Storyline
(from a narrative perspective)
The Gnomes have suddenly invaded Suburbia/Zomburbia, and - in a flash - have banished the plants and zombies from their home. The Gnomes claim Suburbia/Zomburbia for their own, renaming it "Gnomurbia", assuming absolute authority in their newfound territory.
The plants and zombies then find themselves on another part of the world, where - after getting their bearings - they have no choice but to come together and form an alliance to eliminate the gnomes and reclaim their home. Lead by Crazy Dave of the Plants and Dr. Zomboss of the Zombies, they are hoping for a miracle that will make the Gnomish army leave their realm for good.
So begins a long, costly battle to reclaim their home.
Hub World
A new type for hub world where it's continually expansive, becoming larger than GW2's backyard battleground. The Hub World is divided into several areas for the player to explore.
Plants House and Zombie House - Peaceful, calm areas where the player can relax and recharge before his/her next outing. They are equipped with recreational areas for players to do things.
Plants and Zombies Training Grounds - This is where players can try out new characters, do target practice, basic challenges, and more.
The Central Hub - This new location in the form of an ever-expansive battlefield has many new secrets for players to explore. Includes the Flag of Power, the mystery portal, the stickerbook, the sticker shop, and more. Garden Ops, Graveyard Ops, Co-operative Ops, Multi-Ops, various Multiplayer modes and more can be accessed by a single control panel found on either side of the hub.
Online Requirements
No online account or internet connection will be required to play this new GW instalment, making it the first game in the GW series to be playable in offline mode. Families with young children will benefit from this. Some areas of the game - multiplayer modes, online split-screen, player loyalties etc., will be unavailable unless the player as an online connection.
Map Creator
A first for the GW series, maps can be created and edited to one's desired spec. It applies to maps involving Ops mode, Co-Operative Ops mode, Multi-Ops mode, Team Vanquish, Vanquish Confirmed, Suburbination etc. The Hub - and it's smaller areas - can be edited as well, giving players a greater level of freedom.
More Character Variants
Most existing classes from GW2 will return with new variants, such as more Electro/Power characters, more Toxic characters, more Fire characters, more Ice/Frozen characters etc. There will also be a supremely large increase in the amount of variants for each class in the game.
Sticker Shop
The sticker shop comes with a dozen sticker packs, such as:
Mixed Reinforcements Pack - Gives 5 consumables ranging from pots and bots for defense, and weeds and browncoats for the offense against the enemy. Cost - 2,000 coins
Pots and Bots Reinforcements Pack - Gives 5 consumables consisting of Pots for the plants, and Bots for the Zombies. Cost - 2,500 coins
Weeds and Browncoats Reinforcements Pack - Gives 5 consumables consisting of Weeds for the plants, and Browncoats for the zombies. Cost - 2,500 coins
Uncommon Customization Pack - Gives 5 customization items for changing the appearance of your character. Gives at least one Uncommon item. Cost - 5,000 coins
Rare Customization Pack - Gives 7 customization items for changing the appearance of your character. Gives at least one Rare item and a Rare character sticker. Cost - 10,000 coins
Super Rare Customization Pack - Gives 9 customization items for changing the appearance of your character. Gives at least one Super Rare item and has the best chance of a Super Rare character sticker. Cost - 25,000 coins
Plants Customization Pack - Gives 9 customization items for the plants, and has the best chance of a Super Rare plant character sticker. Cost - 30,000 coins
Zombies Customization Pack - Gives 9 customization items for the zombies, and has the best chance of a Super Rare zombie character sticker. Cost - 30,000 coins
Spectacular Character Pack - Guarantees a new Rare or Super Rare character instantly. Cost - 50,000 coins
Legendary Pack - contains 5 Legendary items, also contains Legendary consumables and has the best chance of a Legendary character sticker. Cost - 150,000 coins
Scrumptious/Infinite Pack - contains 5 items and is a mix of Scrumptious and Infinite items to customize your character. Cost - 100,000 coins
Boss Hunt Mixed Pack - contains 15 consumable Pots and Bots to help you in the fight against a tough boss where both the Plants and Zombies must fight against as one team. Cost - 20,000 coins
Boss Hunt Plants Pack - contains 15 consumable Pots to help you in the fight against a particularly tough boss. Only available when a specific boss hunt is active. Cost - 20,000 coins
Boss Hunt Zombies Pack - contains 15 consumable Bots to help you in the fight against a particularly tough boss. Only available when a specific boss hunt is active. Cost - 20,000 coins
Stickerbook
The stickerbook has been revamped, with silver, gold, diamond, gem, scrumptious, infinite etc., versions appear in small boxes sitting to the right of a particular customization item. Minimizes the amount of pages in the stickerbook.
This is basically what I can think of at the moment.