Description of problem:

DNF seems to be lacking many shell completions still.
I'm not sure if this should be done downstream (upstream?) to each shell, but here's the current status in comparison to zypper.

Notice how dnf is the only one to not do anything with shell completion, zypper at least do something, regardless of whether it's contextually accurate for zypper to do so.

Actual results:

zypper in q<TAB> = shows packages (bash, zsh, fish) 
dnf install q<TAB> = shows packages (bash, fish), does nothing (zsh)
dnf in q<TAB> = shows packages (bash), does nothing (zsh, fish)

zypper mr <TAB> = shows openSUSE repository IDs (bash), shows flags (zsh), shows all repository IDs (fish)
zypper ar <TAB> = same as mr
zypper rr <TAB> = same as mr
dnf config-manager <TAB> = does nothing (bash, zsh, fish)

zypper packages <TAB> = shows flags (bash, zsh), shows repository IDs (fish)
zypper info <TAB> = shows flags (bash, zsh), lists all packages (fish)
zypper info q<TAB> = shows packages (bash, zsh, fish)
dnf info <TAB> = lists all packages (bash, fish), does nothing (zsh)
dnf info q<TAB> = shows packages (bash, fish), does nothing (zsh)

zypper in --from <TAB> = shows openSUSE repository IDs (bash), shows all repository IDs (zsh, fish)
dnf install --enablerepo <TAB> = shows disabled repository IDs (bash), does nothing (zsh, fish)

Expected results:

dnf install q<TAB> = shows packages
dnf in q<TAB> = shows packages
dnf config-manager <TAB> shows flags OR shows all repository IDs
dnf info <TAB> = lists all packages
dnf info q<TAB> = shows packages
dnf install --enablerepo <TAB> = shows all repository IDs OR shows disabled repository IDs

Additional info:

If anything, I believe config-manager is the most important out of these, as it's the only thing where shell completion does absolutely nothing regardless of shell.