On a personal note actually, I was doing some roulettes on my MNK last night with this thread in mind, and I think my biggest current issue with positionals is the lack of positive feedback.

As it stand most of the time I don't actually know that I've hit them or not.

Like, if I 'm standing directly behind the boss and I hit a rear positional button, I know intellectually that I've hit that positional requirement, and have thus increased my damage or what have you. But in terms of actual game feel, there isn't much of a difference between hitting it and missing it. It feels very unsatisfying.

Perhaps there's something I'm missing, but I can't actually tell if I've hit a positional other than:
a) I am very obviously in the right position
b) I use some sort of 3rd party tool and review after the fight

I feel like if the Dev team want to keep positionals around one of the best things they could do is improve the visual/audio feedback for sucessfully hitting one.