For what it's worth I don't think the intention is to devalue in December.
If we look at their notice, it seems like they're trying to clarify things for members who are less engaged. Honestly the charts are kind of all over the place, and I would guess most members care about pricing to a region, not pricing for a specific carrier. Hopefully they don't hide award levels for specific carriers though, that would definitely be a step backwards.
Starting late December, the way you view award charts online is changing. We’ll have a simplified award chart to show you where award levels start based on which regions you’re traveling from and to
This portion is a little more alarming, but is already the case today (Qatar, Condor, Icelandair, Aer Lingus's 280k J award etc.). It does suggest that Alaska's future partners might continue this trend which would be unfortunate.
With this change, similar to awards on Alaska, partner award levels may vary depending on multiple factors including route, distance, or demand.
edit: I did just notice JAL and TN went to "starting at" which sucks and I wish they would be more transparent on what that really means