I currently don't use Vampire Bats, I use Plague Bats. However with the leaked ring passives I see massive potential for Firebats.
ItemPassive_Unique_Ring_512_x1 - Enable all runes for a specific skill.
Now I could be reading into this wrong, however I assuming we get to choose which skill we want to enable all runes for.
So our Firebats will have big bats hitting for 220%, A stream of bats hitting for upto 578%, Bats seeking for 350%, Bats swirling around us for upto 601% damage & now with this change we can use this for aslong as we like.
Sounds pretty good to me, although this is very early days and no doubt most things will change.