Thanks for the replies guys. Adding the velocity to the points seems like an incredibly handy way to do it alright, I was just curious if there was a way to get a velocity attribute onto them (bar say using an attribute transfer) that you declare elsewhere. Because I see you can initialize v on the Fluid Source Node. If you have any velocity on the points of the object you create the Fluid Source Volume with then they don't carry across in any way.
I've since recreated something akin to the old set-up with the volume velocity node, and by importing that through the 2nd or 3rd inputs on my Flip Solver using a volumesamplev on a wrangle of Vop, though once the particles hit the bounds of my volume they tend to stop unless I use an enable solver to switch off the wrangle/Vop.
I'm thinking that there's something incredibly simple I'm missing with the volume source node, as I've brought in velocity with that before with the Sop to Dop bindings, and I'm wondering now how you do that now in Houdini 17.