Custom hook to allow plugins for Craft CMS to inject custom "file kinds" into IOHelper. Patch is at very end of snipped IOHelper.php. Example plugin hook at end of YourPlugin.php

IOHelper.php

<?php
namespace Craft;

/**
 * Class IOHelper
 *
 * @author    Pixel & Tonic, Inc. <[email protected]>
 * @copyright Copyright (c) 2014, Pixel & Tonic, Inc.
 * @license   http://craftcms.com/license Craft License Agreement
 * @see       http://craftcms.com
 * @package   craft.app.helpers
 * @since     1.0
 */
class IOHelper
{
	... snip ...
		
	/**
	 * Builds the internal file kinds array, if it hasn't been built already.
	 *
	 * @return void
	 */
	private static function _buildFileKinds()
	{
		if (!isset(self::$_fileKinds))
		{
			self::$_fileKinds = array(
				'access'      => array('label' => Craft::t('Access'),      'extensions' => array('adp','accdb','mdb','accde','accdt','accdr')),
				'audio'       => array('label' => Craft::t('Audio'),       'extensions' => array('3gp','aac','act','aif','aiff','aifc','alac','amr','au','dct','dss','dvf','flac','gsm','iklax','ivs','m4a','m4p','mmf','mp3','mpc','msv','oga','ogg','opus','ra','tta','vox','wav','wma','wv')),
				'compressed'  => array('label' => Craft::t('Compressed'),  'extensions' => array('bz2', 'tar', 'gz', '7z', 's7z', 'dmg', 'rar', 'zip', 'tgz', 'zipx')),
				'excel'       => array('label' => Craft::t('Excel'),       'extensions' => array('xls', 'xlsx','xlsm','xltx','xltm')),
				'flash'       => array('label' => Craft::t('Flash'),       'extensions' => array('fla','flv','swf','swt','swc')),
				'html'        => array('label' => Craft::t('HTML'),        'extensions' => array('html','htm')),
				'illustrator' => array('label' => Craft::t('Illustrator'), 'extensions' => array('ai')),
				'image'       => array('label' => Craft::t('Image'),       'extensions' => array('jfif','jp2','jpx','jpg','jpeg','jpe','tiff','tif','png','gif','bmp','webp','ppm','pgm','pnm','pfm','pam','svg')),
				'javascript'  => array('label' => Craft::t('Javascript'),  'extensions' => array('js')),
				'json'        => array('label' => Craft::t('JSON'),        'extensions' => array('json')),
				'pdf'         => array('label' => Craft::t('PDF'),         'extensions' => array('pdf')),
				'photoshop'   => array('label' => Craft::t('Photoshop'),   'extensions' => array('psd','psb')),
				'php'         => array('label' => Craft::t('PHP'),         'extensions' => array('php')),
				'powerpoint'  => array('label' => Craft::t('PowerPoint'),  'extensions' => array('pps','ppsm','ppsx','ppt','pptm','pptx','potx')),
				'text'        => array('label' => Craft::t('Text'),        'extensions' => array('txt','text')),
				'video'       => array('label' => Craft::t('Video'),       'extensions' => array('avchd','asf','asx','avi','flv','fla','mov','m4v','mng','mpeg','mpg','m1s','mp2v','m2v','m2s','mp4','mkv','qt','flv','mp4','ogg','ogv','rm','wmv','webm','vob')),
				'word'        => array('label' => Craft::t('Word'),        'extensions' => array('doc','docx','dot','docm','dotm')),
				'xml'         => array('label' => Craft::t('XML'),         'extensions' => array('xml')),
			);

			// 2016-12-19 -- IJR -- Added hook to allow for custom file kinds
			// Merge in any custom file kinds from plugins
			$customKinds = craft()->plugins->call('registerFileKinds');
			foreach($customKinds as $plugin => $kinds)
			{
				self::$_fileKinds = array_merge(self::$_fileKinds, $kinds);
			}

			// Sort combined array by label values
			uasort(self::$_fileKinds, function($a, $b) {
				return strcmp($a['label'], $b['label']);
			});
			// END 2016-12-19 -- IJR
		}
	}
}

YourPlugin.php

<?php
namespace Craft;

class YourPlugin extends BasePlugin
{
    public function init()
    {
        
    }
    
    public function getName()
    {
        return 'Your Plugin';
    }

    public function getVersion()
    {
        return '1.0';
    }

    public function getDeveloper()
    {
        return 'RawaySmith';
    }

    public function getDeveloperUrl()
    {
        return 'http://rawaysmith.com';
    }


    /**
     * Custom hook added to allow us to inject a file kind into IOHelper.
     */
    public function registerFileKinds()
    {
        return array(
            'csv'        => array('label' => Craft::t('CSV'),        'extensions' => array('csv'))
        );
    }
}