The developers have said they have a plan for players to fight multiple mobs at one time.
I really do think its a great idea to be able to fight many mobs at ones cuz for me, it gives me the feeling of actually being inside the game. Rather than looking for one monster, kill it, look for another, it's more like actually being in the battlefield and fighting to survive or to reach your goal.
The only thing I'm worried about is that they might make it like Ragnarok Online or Maple Story where everyone just go outside and kill as many monsters as they can by themselves and lvl up. It's really boring that way and there isn't as much challenges in terms of getting your character stronger. If they could keep the same feel as FFXI where instead time, hardwork is needed to get your characters stronger, many of us would appreciate it.
So I'm just really hoping that they can program it that way.