The problem is both side can't trust each other. I suggest a hard fork with consensus:

1. New soft fork must be able to review for a certain time(3days? TBD) before deployed. That is, after top 20 witnesses showed a new soft fork for 3 days, they can really changed to it.
2. Witness voting changed to one account one vote, SP weighted, or any votes as the voters like, divides the original SP to witnesses one want to vote.