Not sure if this is a Dolphin issue, or should be a separate application. Dolphin needs an app similar to gnome-disk-utility. One that allows the user to mount drives and also to mount images, and also write images to usb or disk. I believe gnome also use this app as their gui for fstab.
Mounting drives should be handled by solid, what doesn't work for you? For mounting ISO files there is already another report, please leave a comment/vote there. The other things are out of scope for Dolphin. *** This bug has been marked as a duplicate of bug 175051 ***