Last Updated: November 22nd, 2014
While we weren't able to find anything else particularly interesting (note: Music Key is not linked to this update, previous versions had it, too), YouTube 5.18 does include some interesting strings referring to upload trimming. Specifically, these strings:
<string name="upload_edit_video_tutorial_title">Trim your video</string>
<string name="upload_edit_video_tutorial_description">Drag the handles to trim.</string>
<string name="upload_edit_video_tutorial_zoom_description">Touch and hold to get a closer view.</string>
<string name="upload_edit_video_tutorial_got_it">Got it</string>
It looks like a new upload interface is on the way for YouTube's Android app, and it's probably about time - the current UI is pretty dated.