I would like to see the ability to support multiple controllers for various scenarios:

1. High Availability / Redundancy
  In general, it would be very beneficial to have a hot stand-by in the event of a primary failing.

2. Blue/Green Deployment of updates / Beta Testing

  The ability to put one controller into a "Last Known Good" mode, while rolling out a new version with the ability to Force the updated mode to Downgrade back to Last Known Good would be nice, but I'd be happy if Last Known Good just hung around and took over as primary after nuking the upgraded controller.  And for testing, the ability to put the upgraded node into a Suspended mode in the event a possible issue to detected and let the last known good take back over.  This could/would/should help Support troubleshoot issues by have a differential testing option while not impacting the customer.

3. I'd like to be able to run different versions of the controllers, while maintaining settings across them, but I would also understand if this level of complexity was a no-go and the redundancy was limited to like-for-like.

4. The ability to put specific sites on specific controllers/version would also help with labs/testing

I really like Omada SDN over my previous setup, but after having to rebuild my network after trying to downgrade my controller from 5.12.9 back to 5.9.32 due to issues, this seems like it would be a big win.