I have a couple of suggestions that popped up in my head while playing DR.
1. Make a global chat system, or a LFG chat and trade chat system. It would be nice to have a way to trade and make parties besides using the notice.
2. Command for trade. Ctrl + dropping an item on someone doesn't seem safe (for careless people) and it would be nice if we could simply type /trade xxx. Of course, there would be a need to implement a cooldown, or some way to prevent abuse.
3. Changing weapons based on the individual item, not the item type. For example, if I have a magic vigor dagger and a basic resist dagger, I am able to switch between them with f9/f10. The current system wouldn't do that because they're both daggers.
4. Nerf pepsi blue. It is one of the strongest skills in game because of the slow and increased cast speed. Either that, or make speed potions stackable.
5. The ability to MAKE rare horse/bull/phantom, D1, D2, D3 items. Of course, this would require a lot of thinking, but I think it would be a nice idea. Actually, I don't see the horse/bull/phantom idea being widely accepted, but it would be nice if we could make D1-D3 items.
6. There are a lot of level "gaps" where mobs in one nation are simply not good to go. For example, in Yllse, 70ish to 77 usually goes to bakus as gargoyles, spectres and ogre king pits are pretty horrible in LD. My suggestion is to increase spawn rates for all the non-major pits everywhere. Right now, the pits we have is able to sustain the population, but imagine if we had double the population we have currently?
Just some food for thought.