I am unclear what the purpose is here.
If the idea is to monitor how PWME are getting on I suspect the best way to do that is what I always did for PWRA - I asked them how they were getting on. They would tell me all sorts of different things that mattered to them at the time. I am not sure why one would want anything else.
If the idea is to judge effectiveness of treatment, that needs trials, and is subject to all the problems we have discussed over the years.
If the purpose is to provide 'audit' evidence of a good service then I am very sceptical and doubt that charities should be spending money on healthcare politics games. And rapidly you end up with justification of what professionals like to think helps, without proper evidence.
Maybe there is more to it but I have not seen the proposal. The use of the term 'gold-standard' is certainly a bit of a heart-sink.