Make conforming to the Eclipse UI Guidelines a requirement for participation in the simultaneous release.
I swear that this used to be a requirement, so there may be a discussion somewhere in which we decided to remove there requirement.
Many years ago we added a "Does project conform to UX/UI Guidelines?" checkbox to release records in the PMI. This was not directly associated with the simultaneous release, but does at least suggest that certain members of the community regard this as valuable.