while the idea of no turns is interesting, it could be terrible, simply because of the fact one person could say (for example) 'i swing the sword' 'i block the swing' and just have it go on forever.
the rolls are there to make sure these things don't really happen, and turns just make things a lot smoother and so chat don get spammed
if you have things in place to stop this then it's a great concept, i just see it causing drama and stuff during battles if it's either not turnbased/rollbased
interesting idea over all, not sure how well it'd play in reality, suppose it'd just have to be tested y'know