Excellent article. The fixed plane of motion goes beyond barbells. I have rotating push-up bars and pull-up handles because I find that allowing my arms to rotate throughout the motion feels much better on my joints. Get a weight vest and you can do some fairly good chest work without a barbell.
I use kettlebells for most of my exercises. One of the great benefits is that is forces me to address any asymmetry in strength between limbs. Unlike a barbell, having a separate weight in each hand forces me to do equal work on both sides, eventually leading to balance rather than imbalance.