It might not look exactly the same, but now you can simply use the regular AE motion blur and Particle World applies it like it should.
So on the layer to which you apply Particle World, enable motion blur (tick the box under the motion blur icon, which looks like three circles overlapping.) Forgive me if you know all this and I sound patronising -I’m just trying to be clear. On the other hand if you are new to AE and can’t see the icon, make sure you toggle the switches/modes button so you see all the checkboxes and not the layer blend modes.
You also need to enable motion blur for the composition, by clicking the motion blur icon in the header area above the layers.
It isn’t exactly the same as before but it is definitely a lot more streamlined.
I hope that makes sense.