Au contraire. I'm a fan of the .223 not because of my age, but because it's saved my ass more than once. If the 6.8 had saved me, maybe I'd be an advocate of it. And as I said before, the 6.8 seems a one-trick pony. Deer, coyotes...wait...the .223 can do that. HAS done those. I may be wrong here, but I don't think the 6.8 kills a coyote any deader than a .223.
If I had a few ARs and was looking for something unique, I might get one if the ammo was cheap. Or, I might just paint my AR in a camo pattern for the uniqueness.
I looked at both the 6.8 SPC and 6.5 Grendel and chose the Grendel. The reason is simple enough - the 6.5 Grendel does do something that neither the 6.8 or the 5.56 do very well, perform at long range.
At close range the Grendel has plenty of terminal effect, so the argument that the 6.8 was developed for "close range knockdown power" is moot. From a 20" barrel you can hit right at 2600 FPS with a 120 gr bullet, which I think is about the sweet spot weight for the round. For hunting a 100 gr mono bullet is absolutely not without interest either though. At the mild velocities of the Grendel the 120 gr Ballistic Tip makes for some inexpensive hunting ammo.
With a good 120 gr bullet, consistent 800+ yard accuracy is possible from a 20" tube. I don't think anyone will argue that the bullet selection at 6.5 mm is lacking. That was the main reason 6.5 mm was chosen for the round. Note: I'm not advocating the Grendel as a long range deer round, 400 yards is probably a good guideline for that - but for humans or coyotes it'll work fine at extended ranges. ;-)
Another plus is Hornady is now loading affordable factory ammo with the 123 gr A-max.
The Grendel isn't perfect. The factory mags still sometimes require tweaking for perfect function, although I heard a new first-tier manufacturer was about to come on the scene. I do think the Grendel is very close to an optimal round for the AR platform in terms of killing power, small to medium game hunting, and long range capability.
