FWIW ...

-- snip --
> > What is the recommended upgrade procedure for clients or servers currently
> > running Daedalus?

Having migrated quite a few laptops since ascii, I will now do something like the following when I migrate to excalibur...

>

> I have used the following
>

> # apt-get update && apt-get upgrade && apt-get install usrmerge
> # <add excalibur repositories to sources.list>
>


apt-get dist-upgrade --download-only -y

> # apt-get update && apt-get upgrade
> # apt-get dist-upgrade
>

-- snip --

This ensures that if the following 'apt-get upgrade' breaks your network you at least have all the packages available locally to complete the migration.
I have had this happen with changes to packages borking laptop Wifi, but it doesn't hurt to play safe migrating servers either.