I haven't been following the detail of this, I will admit, so don't know the ins and outs, but my feeling is that it is possibly good progress, though like the OP mentions, it may be too restrictive in some cases, with the 6 month "window", but at the same time any such law needs to protect those from using it "just because" or misuse.
From personal experience, one of my grandparents spent the last 9 or so months of their life between care home and hospital and generally speaking was bed bound (this was having lived a fairly active life up to that point). Mentally they were very much with it (unlike another grandparent who suffered for years from dementia, but was physically ok/was mobile) and I know they were incredibly unhappy and hated "being moved around like a piece of meat" with no prospect of improving. Notwithstanding this, when the time eventually came for palliative care (off the back of double pneumonia), all fluids etc were withdrawn and they eventually passed 5 days later, though out of consciousness for all bar the first few hours. To have to go through that is awful, to be honest.
From my point of view, having seen the likes of care homes (vice residential homes) I have zero desire to be resident of one, particularly should I end up like my grandparent did in the last few months of their life and would probably rather go peacefully and on my own terms.
EDIT: I forgot to add, there is no way I would support something like this going to a referendum - we all know how well they work for the biggest decisions going...