I think it would be good to add a comment and changelog explanation that this is only there until there is a clear way for maintainer scripts to copy the /etc/default file in as an override in order to deprecate it.
You also need to set a default value for the options with this:
env libvirtd_options="-d"
So that the default file isn't needed at all anymore.
Couple things that I think need fixing here:
I think it would be good to add a comment and changelog explanation that this is only there until there is a clear way for maintainer scripts to copy the /etc/default file in as an override in order to deprecate it.
You also need to set a default value for the options with this:
env libvirtd_ options= "-d"
So that the default file isn't needed at all anymore.