I think the game has few roleplaying elements. Few things affect the gameplay apart from class and race (and other traits like feats). Would it be too difficult to make NPCs react to the characters according to other factors, like alignment or even gender?
(BTW, I think evil alignment doesn't need to be forbidden. Many evil people works for good patrons, work for a better world for themselves and even think of themselves as good)
Also, background options could be nice for this. Things that define the characters and can be used to advance their stories, like a job as mercenary, rich/poor family, some special circumstances of birth, or even a forgotten childhood (which could lead to other random background options).
NPCs might behave as friends, rivals, colleagues, extended family or even love interests of the PCs, including Hirelings, and the interaction between them be a reflection of this relationship, like a variation of prices, presents or a bit of backstabbing (a hireling obeying "less than optimally")
In addition, some NPCs could be able to be unlocked as hirelings, depending of their relation with the PC (they could be called Followers and, in certain quests, they give Optional Objectives or otherwise advance the storyline) and some of them will only give quests to certain characters. If a character can't receive a quest from a NPC, (s)he can always join the party of someone who has that quest (sometimes the objective should imply the main character actively being part of the resolution).
Also, some kind of NPC-based guilds could be good (a character can join both one of them and one created by other players), could give specific quests and be rivals with other guilds. They could confront each other in Challenges (dungeons in which 2 parties have opposite objectives, like being the first to get an item, collect the more of another item, a pursuit, trying to kill/protect a NPC, negotiate with another NPC to favor their guild...)
Any thoughts?