For that as said you will need to open a feature request to KDE.
Maybe if this is an important part of your workflow, and what is possible with Dolphin isn’t working for you, try to find a file manager that has the features you require.
//EDIT: also you could reassign a mouse extra button to keyboard keys combo (like ALT + Up Arrow or something else), and change the shortcut for parent folder in Dolphin to that keys combo. For example I use evrouter (an outdated piece of software that still works to this day) and imwheel to do this kind of stuff with my mouse as there is no official support from Logitech.
//EDIT2: apparently there are tools like Key Mapper Input Remapper which are recent and maintained that could do that if you have extra mouse button you would use for that specifically.