A couple of points:
Pkg has no problem with duplicate names, so squatting a name like this does not prevent someone else form using it. It prompts for which you want and in the future we could provide download stats and/or stars to help people decide. I doubt an empty package will get a lot of stars or downloads so it would not take long to rank higher than a squatter.
We should actively archive unmaintained or empty packages. We have already done one round of this for packages that don’t support Julia 1.0 at all; more archivings can occur in the future.