In an era of watts-fests, do we really need races to become even harder and more attritional? It's not like anybody finishes Paris-Roubaix with energy to spare. Adding 30km would make it as long as Milano Sanremo and multitudes harder.
I see your point re the break, but I think what is more likely is that the makeup of the break is weaker as big teams will be more cautious, or that the break goes after a very, very extended fight (making Paris-Roubaix even more attritional). Back in the days of Terpstra attacking out of a fifteen man group maybe that made sense, but nowadays? Wouldn't it just lead to even longer solos and tactical battles than end after the first hour?