User blog comment:DaNASCAT/Technical Update: September 11, 2012/@comment-3030984-20120911173428/@comment--20120912164158

All, we will not be cutting down on content space for wikis in so far as I am aware, we are tweaking all parts of the skin modules' width, hence where the right rail may be perceived now as cutting into the content area, it's fair to say we will be adjusting other areas to keep the content space you have.

I do know this affects some custom CSS now, and that when the wider implementation of this comes out fairly soon it will affect some CSS then too. The reason for the inconsistency now is that the features you are seeing the extra rail width on is because those features are in active development, and it's simpler to add it in now to the design than rewriting the design later.

I know wikis work hard on CSS, so I won't pretend the CSS concerns are trivial, but at the same time the goal of all of this is to make the skin more grid-friendly to keep up with web standards and to make element sizes and proportions consistent. Hence, even though it will affect your CSS now, I anticipate this will simplify your CSS coding needs in the future.