You accountants/consultants/advisors love to quantify things, but I'm afraid the backlash to a no-notice devaluation, system wide or not, to one of the-if not the--most aspirational awards on your chart can't be quantified at this point. While theoretically possible to insulate the MVPs from the deval, that's not what AS chose to do, and are, in effect, throwing out the baby with the bathwater--regardless of whether they can "recognize the expected decrease to their mileage liability as income almost immediately."
That's exactly my point. Since it's difficult to quantify (albeit not impossible to estimate, as you suggest), I wouldn't be surprised if AS is using the lowest negative impact they can justify in their models. And, I'd hope they would have conducted this analysis before deciding on the devaluation, so they'd know exactly what that impact would be before deciding to devalue. Meaning, from a bottom line perspective, this change will likely have an immediate positive benefit, followed by an unknown future impact (that AS probably believes will be positive).
And again, this may be "one of the-if not the--most aspirational awards on [their] chart" for us, but I'm not sure the typical business traveler has the same aspirations as we do. AS should have the data to project how many frequent flyers (vs. frequent churners) would be impacted, and I would hope they made a decision based on that data. If, for example, 50% of churner redemptions is for EK F but <5% of MVP (through flight) redemptions is for EK F, the no-notice might not cause as much negative backlash.
IMO the bigger issue here that would impact the entire program is the precedent of a no-notice devaluation. AS may be banking on flying below the radar and hoping their most profitable customers don't realize what they did. I'm not sure whether this will work.