1) As a stopgap for Particles and Volumetrics, a full featured implementation of OpenEXR 2.0's new Deep Data feature would allow you to more easily comp those passes generated from other sources. If it was a choice between having OpenEXR 2.0 in 6 months or Particles/Volumetrics in 12 months, I would opt for OpenEXR 2.0.
2) Please consider (if technically feasible) adding OpenVBD or Fields3D support when implementing Volumetrics.
3) Multilight in Octane would be really intriguing and I think *all* users would enjoy this feature.
@OctaneTeam: It's not a fair 1:1 comparison but it is interesting to note that Maxwell 3.x will be shipping with many of the features mentioned in this poll (Volumetrics, Multilight, OpenEXR 2.0, OpenVDB, OpenSubDiv, improved Hair/Fur and Motionblur performance).http://vimeo.com/77637411
^At the very least it may be helpful to see how they handled those features into Maxwell 3.