I'm not level capped yet, so this is slightly ignorant but, there should be passive skills, i don't know if i have passive skills i haven't leveled yet, theres no way to tell, the descriptions are slightly vague but there should be.
The games not massively complicated, so i doubt it wouldn't be a struggle to implement a "stone" of kinds, that will imbue (permanently) any piece of equipment your avatar has, with one of the 3 attributes, (STR DEX INT) and maybe they could have levels, i.e, small, medium and large "stone" ranging from +1, +2, and +3.
On the same note as the "stone" idea, a "stone" that could increase a weapons attack value, by a certain degree, also this could be applied to armor aswel.
Obviously a trading system, theres already items that are being picked up by the wrong class/build etc and their simply sold, never seen again. We can click on an avatar and view their stats, could there be a shop system implemented so that we could shop as we go, a new tab on an avatar which shows what their selling?
A small map, or a few (if indeed a trading/shop system is implemented) that we could go to just to view each others wares.
New equipment, a new tab for a ring or necklace, i understand the menu would probably have to be re-organized or change completely to accommodate new tabs etc (i'm using an iPhone), all the tabs are pretty crammed together, it would be nice to be able to switch tabs via a d-pad system, or no tabs at all! you simply swipe to access the next page, would definately make it easier and more spacious.
