As soon as Google's latest version of Android came out we were eagerly waiting for the S4 mini to get updated by the end of 2013 since it was a new device.
Unfortunately, that did not happen and since then there have been many rumors spreading around with lists but this time we might finally have received legit proof thanks to a Samsung insider who has leaked an internal document with some of Samsung's device software updates and the most important part, ETAs. As you see in the document below, only the 3G and LTE models are included and the Duos is missing which is pretty strange. The LTE model seems to have passed the tests succesfully and the 3G model is also nearly done.
There is no information regarding any UI changes unfortunately. Whether the update will include Samsung's updated TouchWiz looks, we don't know but chances are it will probably look like the Galaxy S4 when it got updated with just minor changes such as white status bar icons. (Just my personal speculations).
Thanks to SamMobile for the information.