TYPO3 Core

I am working on a Typo3 4.7.1 platform.

For the display of filetypes in content element "File Link" (and elsewhere) I am missing icons for the filetypes docx and xlsx which have become widely used, instead of xls and doc.

Could such icons be included in future versions?

----------- Here more details, and what I tried to solve the problem locally ---------

On upload of a .xlsx or .docx file for display in FE in a "filelist" content element, those files get displayed as expected, but without the respective icon to the left of them.

In an attempt to solve this issue I first created two fileicons called docx.gif and xlsx.gif and put them into the typo3/sysext/cms/tslib/media/fileicons folder.
I also put them into typo3\gfx\fileicons (for the Backend).

Then I updated the tables.php (sitting in t3lib/stddb) where file types are associated with image files to be displayed as icons. I added the lines
'docx' => 'docx.gif",
'xlsx' => 'xlsx.gif",
(This is approximately in line 400 of the tables.php)

However, anyway, on upload of a docx or xlsx file, the Backend shows an alert "No thumb generated" instead of the expected file icon, and in Frontend there is just nothing.