Sorry, I thought you were patriciaruth when I wrote my response!
You're the one who did not acknowledge my point that a devoted spouse's willingness to care for an incapacitated spouse may change over the years. I thought that was a crucial point. You ignored it. And, I still think it is a crucial point, that a spouse's desires for a new spouse may alter the situation and necessitate a change of legal guardianship, while a parents' desire to care for their incapacitated adult child may be less likely to change, since they are not trading in this child for a new child.