The problem is, Mein Kampf is already easily accessible (you can download it from the internet in a matter of minutes), so I don't think copyright expiration would matter much.
Mein Kampf is incredible poorly written and boring. It will never be a bestseller, even among the far right.
Have you ever tried to read Ayn Rand?
No, Mein Kampf is a highly influential work so I forced myself through it. I could never mobilize the same motivation to get through any of Rand's drivel.
I salute you. I've tried to go through Mein Kampf twice, but I just couldn't go far. Regardless of it's disgusting political context, it's really awful read.