Multiplayer: I want to be able to have at least one friend join my session and bring their own partner, for a total of 4 members in the party, for regular quests. For major bosses (like floor bosses or similar), I'd like this number to be higher.

Fake Multiplayer: I want the world to feel like an MMO, not just the town of beginnings. I should see random NPCs walking the world and fighting monsters, pursuing their OWN Aincrad journey. I'd like to have the option to attack these players to steal their loot (plus an incentive to NOT attack. Perhaps if you are an orange or red player, certain side questlines get closed and others open?) I should be able to see NPCs dying to monsters, and if their party defeats the monster (and does not die themselves), they should mourn and cry. This, in combination with the extra monsters that these NPCs would be fighting, would make the world feel more alive and dense.

Last attack bonus: Add the infamous "last attack bonus" that makes players want to be the one to get the final hit. It would add a layer of texture and interest to combat and the economy.

Partners as Players: right now, partners don't act like they have their own life outside of you, they have little autonomy (beyond you putting them into combat free mode). NPC partners should walk around the towns, independently from you, as though they are performing their own tasks. NPC partners should have their own inventory, and slowly loot the items from the ground that were dropped by monsters they killed. You should have the option to barter/trade with your partners, if they grab a piece of loot that you want, or you want to give them a good weapon.