"If most projects had a clear ROI (as measured by $), leaders wouldn't get the big bucks they do because decisions would be easy & judgment would not be required." Kudos for that, Jim.
So, yes, a clear, compelling, ROI makes decisions easy. Your job, it seems, though, is to implore your CEO to consider a less-than-easy decision. To that end, it's often helpful to consider what your CEO "listens" for. (Some bosses listen for problems to be solved; others listen for opportunities to leverage.)
If your boss listens for problems to be solved, framing your initiative as an opportunity will likely get you nowhere -- even with a clear, compelling, ROI. But if a problem exists that's creating significant and ongoing risk, the probability of a listener-for-problems-type boss listening to your concerns dramatically increases -- especially if you can show how the problem, if left unmitigated, is poised to significantly increase organizational (and political) risk/exposure.
That the CEO wants consensus just means that you need to notice what your peers listen for, as well, and talk with each of them, individually, in those terms before having them vet your ideas as a group. Consider it "advance" work, setting the stage, building consensus, etc. If your recommendations are important enough to you, doing so should not be a problem.
Hope this helps.