I have exactly the same question! How do we apply for any branding features, especially for those that have already had the "all videos monetized" feature for a long time? I've had a monetized account for over a year and never applied for partner because I wasn't sure I met the qualifications view/subscriber wise. I finally decided LAST NIGHT that I would put in an application for partner today seeing as my views & subscriber numbers had been climbing - only to find that they "did away" with the partner program a few days ago!
I'm so disappointed! All I want is to be able to upload my own thumbnails... I'm tired of these crazy pictures of me as my thumbnail!