You don't need cooked fish to kill Eikthyr, that is a silly concept and the reasoning behind why you can't just instantly craft a rod (as well as why you need a kettle to break fish down now)

As far as harpooning goes the simple reason is the bait system would have no reason to exist if you could spear whatever you want out of the water. Some can argue that the bait system is silly and that's fine, but at the end of the day fishing is a completely optional activity for those that enjoy it.

So if you are sitting waiting for a change to the fishing system to let you craft rods or spear/harpoon fish, I am extremely doubtful it will happen. It would not make sense unless they completely revamped the system.