So, really, why not implement the creation of custom buttons in dolphin. Example use case and code here: https://forum.kde.org/viewtopic.php?f=223&t=140139 So in the example you can have a button that plays all the files in the folder. If you bind a keyboard shortcut to that button it will be even more powerful, in my opinion. May not be too simple to actually implement but I find it as maybe the most powerful thing you could do in dolphin in one shot.
*** This bug has been marked as a duplicate of bug 385303 ***
@RaitaroH Hi :) You can vote for the duplicated issue, in order to show interest. Its also possible to announce this in the forum (I keep away from it since the login system bothers me heavily.) Thanks a lot for your input ^-^