One potential problem with duality could be that it ensures the most efficient distribution of duties as the parties have fully supportive functions, but is seems to me that there could be lack of common interests and things to talk about that could cause problems in the long run.
Well put. That is most definitely a HUGE barrier, especially in the begining stages of development. But given enough time together, duals start to realize that they understand one another on a subconscious level, and therefore words are more or less meaningless. Actions are what matter to dual pairs, which is why you can say incredibly offensive things to your dual after knowing them for a few months and they will not be offended, but will rather laugh, because your dual will almost NEVER say something that burns them to their very soul (affecting weakest conscious function). Duals know how to tease the other without saying something that will truly hurt, although that does not mean that there is no pain in such realtionships. I myself have caused great emotional pain to two ESFjs that I have known, but only because I could not bring myself to commit myself to a relationship with one of them (as hard as it was for me to do). And the other because we were living together and we'd have all the emotional dynamics of a married couple (even though we weren't dating one another) but none of the physical aspects. This formed sort of an incomplete duality that frustrated the hell out of me, and caused me irritation, even though I was as guilty for not creating something more, as she was. It's a fantasitc relationship, but it's not always perfect. And there are so many environmental facors to account for that it is rare that duals have the opportunity to spend quality uninterrupted time together giving them the chance to begin forging the relationship.