The era of "middle class" ended long ago, when dad lost his factory job and mom had to go to work to "supplement" the declining real income.
Perhaps you're right and that was the "peak" of the middle class. But I suspect we have a long way to go. Wealth will be concentrated among a small number of people (as it mostly is today anyway), and the rest of us will be back serving as low-paid and low-class servants, farmers, lumberjacks, boatmen and milkmen. If we're lucky.
Time to watch Masterpiece Theatre and brush up on my hat-tipping and groveling.

Seriously though, I agree that the loss of high-paying, blue collar jobs overseas has already hurt the middle class, but I also suspect that high-paying, white collar jobs, like mine, are going to be scarcer in a post-peak world.

Study with an expert and watch Anthony Hopkins in Remains of the Day!

With less energy supporting our society, we will lose a layer or two of complexity in our economy, and complexity is what gave rise to the populous white-collar class.

I'm already experiencing what this will be like myself. I'm a former globe-trotting, big city corporate communications manager now living in rural Vermont. It's quite a change. A lot of the people around here are very self-sufficient, and get by on very little compared to city and suburban folks.