There are many days that I get disheartened about graphs being too complex to use as an interchange format. My world (structured data at Google) revolves around graphs but humans just have a lot of problems reasoning about higher dimensional data. Sometimes I think trees are about as far as the average person can handle intuitively.

I can easily point to all the advantages in composability, lack of redundancy, etc. but if you can't picture it easily in your mind it makes it hard to work with.