This is an important and timely discussion to have.
On the 2-step submission system – I think it can work very well but it is an additional work that we would ask the authors to engage with. Why should they do that when our agenda is always constantly packed? 
Maybe it is more meaningful if associated to a NIME journal? In that case, authors would be motivated to dedicated further time to improve their paper taking into account the received feedback.
On the rolling submission process – big thumb up here but possibly not for all sort of submissions. We might identify what sorts of submission are meaningful to be published on a rolling basis. I believe that some submissions would not benefit from an outside-of-the-conference rolling publication, particularly those that might result in high discussions. This year’s conference (especially due to its hybrid format) proved once more that the conference setting can offer space for in-depth discussions. Examples of submissions that can work well on a rolling-basis:
- Updates on existing NIMEs presented at previous editions
- Evaluations of commercial DMIs (being timely on this can be very important)
- Technical “innovations” that other communities members could benefit from
- Debates on hot topics
- Book reviews (not sure)
…