I'm really hoping that in some of the writing apps I use (Ulysses, 1Writer, Notes) the touchbar will be customizable to include special characters. I work with ancient languages, and some of the special characters I type don't have easy keyboard shortcuts at the moment. Being able to just dock them above the keyboard would be a dream come true!
I would love to see Tweetbot add support for the TouchBar. Also LastPass support would be great. I saw 1Password update to support TouchId and I may look to switch.
I would like to see spotify support, kind of like in the images released before the new macbook was announced. They showed the song and artist currently playing on spotify displayed on the touchbar.