Why are Middle Name(s) not supported in WordPress yet?!
It is a simple thing to implement, as I have done in a local WP install of mine!
I came across the idea, when I was doing implementation of the Open Graph Protocol in a theme I am in the stage of developing. And in the search process for different WP tags (via google) stumbled across a thread one started years ago in the WP.org forum (cannot find the URL for the thread now...). Where a person complained a bit about the missing option for use of middle/(additional) names.
An excellent opertunity to use middle/additional names can be illustrated with the OGP protocol: HTML coding -->
<meta property="og:profile:middle_name" content="some middle/additional name goes here" />
And in the process of implementing middle/additional names in the wordpress core, for use in the wp profiles. Why not implement the option, in which order the names are to be shown (when used as the display name!!!)
NB: A similiar suggestion for middle/additional name(s) can be seen in the WordPress Trac.