Comment by WA

The same argument would apply to any other kind of will or testament. You need to update it frequently. It’s not uncommon for people to change their mind quite late, and (at least in Germany) that’s perfectly possible even until late. If people dispute this later change of mind a judge needs to get involved, and being married to one I can tell you that they treat each case differently and with the appropriate care.

Arguably the best qualified person to decide what to do with Future You is Present You.

Uh, new years resolutions are not exactly what I would call the ideal metaphor for assisted suicide.

Plenty of people here who reacted negatively to OP's suggestion seem to not have had to deal with a loved one who dealt with Alzheimer's or other forms of dementia. It's not hard like taking care of a toddler is hard. It's hard like, "this is not the same person I know for my whole life, they don't recognize me, they say and do mean things to me and their grand-kids and neighbors all the time, and require 24x7 supervision to not hurt themselves or break everything in the room."

Oh, and remember that in the US, all nursing homes for this kind of thing are for-profit companies backed by venture capital, meaning they are expensive as hell. Take your current middle-class apartment, shrink the size to just a bedroom (that you now have to share with someone else), and then quadruple the rent. Just a few years of that can decimate the life savings of the average retiree and/or their children's.

I speak with some authority here because all of this happened to my father. He was "alive" in the last few years of his life, but not what anyone would call "living." I absolutely do not want that to happen to me. If it were legal in the US, I would absolutely opt for an assisted suicide plan for myself.

There are ways to handle it that avoid all the "whatabouts" that you and others have already brought up. One rough draft of an example: 1) Have a lawyer write up a kind of will expressing my wishes. 2) Get three unbiased negative diagnoses to show I am of sound mind prior to signing the will. 3) Go in for regular testing (every year, maybe two). After each negative diagnosis, add another (witnessed and/or notarized) signature to the will. The will is not valid if testing or a signature is missed. 3) If there is ever a positive diagnosis, it must be confirmed by two other clinics. 4) If three years pass with doctors and clinical tests confirming increasing dementia symptoms along the way, the assisted suicide clause is invoked and I get to pass peacefully surrounded by loved ones instead of being a stressful burden on them for years or decades to come.

Yes, there are details and unintended consequences that neither me nor anyone else can see ahead of time. Like everything else, they are dealt with as they come up. No, you won't convince me that your favorite corner case means the entire idea is invalid.