It appears that gmpc no longer has any sort of upstream developer.
https://github.com/DaveDavenport/gmpc is specifically labelled as
unmaintained, https://repo.or.cz/w/gmpc.git hasn't been touched since 2015,
and the former maintainer's domains sarine.nl and gmpclient.org are
domain-parking placeholders.
I am already a single point of failure for too many things, so I am not
able to become the new upstream maintainer for this. Is there anyone else
in the mpd team who could?
Next time there is a problem that is not trivial to solve, we are
probably going to have to deprecate and remove this package, for example
in favour of sonata (which is also looking for a new maintainer, but at
least it still has somewhere for that announcement to appear).
smcv