I doubt this will affect all but a very few AE members who are moderate travelers, and may only really affect those who've taken a flight or two every year or so and kept collecting and never used them. But since this is a rolling backdating, the churn of miles earned and used will end in a wash for 99.9% of AE members. Perhaps some SEs are earning so many miles and not using them enough to retire those earned 7-years ago. But you're pretty much making a tempest in a teapot about much ado about nothing.

At present, AE factored its "breakage" rate a 17%. That's the number of miles that never get cashed. For accounting purposes, some limitation had to be applied and the industry as a whole has adopted the 7-year rolling backdating.

Most US programs do indicate expiring miles because they've had this in place for a few years. AE will likely add this next year when the first year of the seven starts expiring. But again, I doubt that this will affect very many people, since all inactive accounts will be terminated, and people have been reminded about expiring accounts 6-months in advance, and inactive accounts have mostly been written off.