Hello,
Ok so I've been playing with the particles trying to create goo/oil monster. That requires a lot more control over the flow of the particles.
The bounding box is perfect for control, but when I move the particle source it looks like an invisible wall is pushing against the particles lagging behind.
So basically adding a drag option on the lagging particles will let the particles to go slightly outside the bounding box (with ease in and out) and allow for a smoother flow.
Hope this gets added, it will allow for more possibilities with particles.