Personally, I am not going to bother with DDR4 until 16gb sticks are widespread enough. Maybe a couple of years from now.
Also, if you are into high-res photo/video editing, extra ram is always handy.
I agree to a point. I would be unwise to tell anyone what their needs are. I've often wondered about folks who insist on having 32GB. Or -- more . .
I might also mildly agree with Harry_Wild. With 2x8GB, and various (and concurrent) usage, I don't see myself "running out of RAM."
But now, I wouldn't be satisfied with just 8GB. There IS a very good use for the ample surplus above that in my systems. I have RAM-cached SSDs on every machine but my server. One laptop is limited to 8GB, only needs about 4 to 5GB maximum for just about anything, and the remaining 3GB caches a drive connected to an SATA-II controller. With those limitations, it actually makes quite a difference.