Tested with Gwenview, Konsole, Spectacle, and Kate in a new user account after deploying the change. Here are some before-and-after screenshots:
Gwenview Save dialog, before:
{F5804774}
Gwenview Save dialog, after:
{F5806365}
Konsole save dialog, before:
{F5806388}
Konsole Save dialog, after:
{F5806368}
Spectacle save dialog, before:
{F5806377}
Spectacle save dialog, after:
{F5806383}
Kate save dialog, before:
{F5806371}
Kate save dialog, after:
{F5806369}
It seems like a straightforward improvement for the common case where the {nav Save} dialog has a combobox for choosing the file type. However, Kate has a weird filter box instead. I wonder if having a filter feature even makes any sense when saving files, and if it does--why only for Kate? If necessary I can make the string return to "Filter" for these save-with-filter dialogs, but I'm still left wondering what the feature is actually for or if Kate is affected by a bug that should be fixed...