Not sure where this notion that mentally ill people could be 'offered' AD has come from regarding the uk bill.
I presume the very limited criteria to 'qualify' rules out those who are not deemed 'sane'.
On a philosophical level, i think anybody should be able to control their own life, even those suffering depression. Most people diagnosed with a long term debillitating illness will also suffer from depression once their future is laid out before them (my mrs was suicidal on and off for a couple of years).
In fact, i'd say that somebody knowing a process is in place for when/if it all comes on top would look at their future in a slightly more positive light.
Saying all that, i think mental health issues and physical health issues shouldn't be lumped in together regarding AD.