I can't recall if it was you who asked about the reservation and the park filling to capacity, or someone else, but I think that question recently came up in the Superthread (which I know you follow).
I don't think the capacity issue will be a factor until post-12/25, honestly. I mean, sure, it will be quite crowded and it's always possible that capacity could be reached on 12/25 or prior, but I think that 12/26 through 12/29 would be the days to worry about in terms of capacity.
If you have a reservation, that will likely have little to no effect on being allowed in once the park reaches capacity. If it's at capacity, it's at capacity, and no one else is getting in until people start clearing out.
So, if you're planning on eating at BB on 12/26 and beyond, just get to DL early and stay there. Don't leave if you want to be sure to make the reservation time.
Of course, if it is raining or if there is a solid chance of rain, that will scare away a lot of people.
Plan the things that are most important to do. Make a back-up list in case the first list of things is too tough to accomplish in all of the crowds. Spend a lot of time at the 3 hotels, enjoying the décor and atmosphere, and Downtown Disney as well, if
Disneyland gets too crowded.
Take advantage of any EMH or MM you may have access to.
It is less likely that DCA will reach capacity, although it has happened.
