I went back and checked Batman Dark Knight Archives #8 pricing in December and it's $59.99, so it looks like this new listing is the first at the higher price, which supports my notion that DC is giving us some extra pages to justify the higher cost.

I wonder if this means that any potential Done-In-Ones that come in at a substantially lower page count might be priced lower as well?

I'll have to take a look, but I don't believe that's the case with the price increase on the Marvel Masterworks side.