[rloc]

Happy to contribute :

You can't customize the app buttons unless it allows you to which is not the case with Spotify.

1/ display the same touch bar UI when the app is in the front or background otherwise it's confusing.

2/ keep the spotify controls visible when using chrome for example (chrome doesn't have any touch bar controls yet). Right now I have to click the newly added spotify shortcut all the time. Maybe a way to decide which app should be displayed when the space is unused would help (in the OS settings).

I like the song play progress bar, it would be even better with the current and next artist/song names and covers.

[sleepybrett]

BetterTouchTool seems to be coming to the rescue here.

https://www.boastr.net/second-touchbar-alpha-available/

I haven't played with it yet, but it looks like as long as the thing you want to do has a hotkey you can use this to make touchbar button to do it whenever you are in that particular app.

[binaryabyss]

It's pretty great, actually. You can also set it to run AppleScripts, which can call the shell. I have set up buttons in the touch bar for common tasks such as zipping an archive without .DS_Store crud in Finder, and for AirMail I have a button that creates a folder based on the subject line of the open email thread and saves attachments there. I have no idea how the Touch Bar is supposed to be useful by default, but I'm finding it quite nice with some work.