I'm sorry, looking at my first post, I guess I wasn't completely clear.
Although I appreciate nice weapons, I don't really consider myself a "gun-nut." So, pardon my limited knowledge. I own only one firearm, a Sig P229 in .40cal for home defense (and occasional target practice). I have politely declined getting a CCW despite many of my friends and family urging me to, several of them being law enforcement. I just don't go where I feel I would need a weapon. I know, you never know, but I prefer to try avoiding trouble.
Now that you know a little bit about my general feelings towards firearms, you might be wondering why I'd be interested in an assault rifle at all. Frankly, it is because I don't trust my fellow human beings. My work involves emergency planning and the thought of adding a rifle (and probably a shotgun as well) to my personal plan has been stewing for some time. When the Masada/ACR came on my radar from Futureweapons (isn't Mack great?), the idea of a weapon that could chamber the two most common rounds on the planet, 5.56 Nato and 7.62x39 (I assume anyway), caught my eye. I'm sure the 6.8 and 6.5 Grendel are great rounds, but I don't imagine I'd really notice a difference. I liked the concept of the ACR as a weapon that could fire the ammuntion I would most likely be able to find in an emergency: 5.56 and 7.62x39. Whether that emergency is a dirty bomb forcing the evacuation of my nearest metropolis (which happens to be Detroit), or a power outage affecting 1/2 the nation where people don't behave as well as they did last time.
Essentially I want a firearm that in the HIGHLY unlikely event of complete social breakdown that can chamber whatever ammunition is readily available (which I feel would likely be 5.56 and 7.62 Russian). Maybe that sounds paranoid, but I'd rather be prepared than, well, the alternative.
I hope that long block of text gives you some insight.