The reason for the airspace role back was due to lack of risk assessment turning C into E above D; ie the risk was/may have been raised without evidence of the cost benefit analysis being positive. ie you can increase risk if the cost of doing so is achieved or bettered...
Still with me...
So turning G into E is a safety improvement... therefore, you do not need the CBA. So it will be perfectly acceptable to have E over D where G currently exists; cause it's G now, E = safer than G... But just because you can doesn't mean you should. Surveillance makes E so much simpler.
The big issue is ASAs ability to staff the new facilities plus getting the new/old establishments online within the time frame. Then getting the enroute individuals trained to cope with the new E steps and the new procedures associated with the D airspace is a whole other issue.