I'm not on the road anymore so I have access to the keyboard to build this up. I do have it as a backburner task. One challenge is the fact that user Arpeggios are not part of Soundmondo. Therefore, I want to fit the example within the context of the existing control arpeggios that I alluded to.

All I can say right now is that after the control ARP finishes its modulation (non-looped) the assignable knob will return to its original position. Some simplification I stated about using Mute 4/4 and implying this would keep the knob at the "last" position of the control ARP is not true. That doesn't mean it's not possible - only that your control ARP needs to offset the assignable knob at the maximum at the beginning and then at the end of the control ARP end up in the same place as the non-offset setting of assignable knob. Since, unfortunately (and I've asked for this) assignable knobs cannot be directly manipulated through SCENEs - you may need to combine moving the assignable knob by using superknob which allows for setting in scenes and can move a particular assignable knob to a desired location.

So the high-level rundown would be:

1) Default saved Performance superknob position sets the assignable knob to set the Part volume wherever it should be at the start of the tune. Default (starting) scene arpeggio can be Mute 4/4. Say this is scene 1.

2) Scene which does "smooth" volume transition does two things:
2a) Turns superknob so assignable knob which is tied to Volume will be set to the final volume you are trying to reach
2b) Control Arpeggio is changed which will offset this same assignable knob back to the original assignable knob setting in 1st step.
3) Control Arpeggio, over time, moves the assignable knob from an offset value (at the starting volume) to a zero offset value (to the new volume level desired). This way when the control arpeggio (non-looping) ends - the knob will be left where you want it. At the new volume position.

You can extend this to do different transitions (volumes going from soft to loud, loud to soft, fast or slow, etc).

I'm going to, eventually, use preset arpeggios to accomplish the task so a Soundmondo Performance can be "plug and play" to get this together. However, in practice I would probably use a custom User arpeggio. The downside of the given options of the current Arpeggio editing tools (pattern sequencer or performance recorder) is that neither gives you precise control of the events like Motif did. Therefore, it's probably easiest to start building this user arpeggio using a MIDI editor and importing it/converting to a User Arp.