I have added a ton of new features during the lifetime of ST3 and unfortunately it shows when you look at the user interface. So one of the main areas I will be working on in version 4 is to build a user interface that makes all those features better usable.

Let's take a look at some of the things that I think are working fine with the current user interface:

Stage Traxx is usable even on iPhones. Most music apps don't even work on iPhones. There are some elements missing or might be really small, but you can get by with just an iPhone.
Being able to hide the song list in the main player and even change the width of the song list.
Configurable buttons was a good idea (although the number of these buttons must increase)

Of course there are also things I am not satisfied with:

Popup lyrics view: I thought that having something that resembles the interface of the Music app or Spotify would be a good idea. But it makes things a lot more complicated and this popup view caused some major headaches in the last couple of years.
Use of horizontal sliders for everything wastes valuable space (for example the song volume slider in the main player)
Audio regions are poorly integrated into the player
Many things can be done in different places in the app (for example setting the song color either in song details, or in the song properties popup in the main player). Ideally there should only be one place to do one thing
The app does not feel like a native app on macOS.

I would like to build upon the good things and try to get rid or at least improve the bad things.

So my vision would be a single screen application like for example Logic Pro. You only have one screen you work in with panels that can slide in and contain editors for different stuff. So on the left hand side you could have the song list like in ST3. On the bottom you could slide in anything that is related to the selected song like multitrack mixer, equalizer, audio region editor or even a view to trigger audio regions. On top would be your playback controls, and icons to toggle the song list, the settings, the bottom panel and so on.

Problem here is: this setup will not work on an iPhone. And here I am really not sure what to do. Should I concentrate on the best possible big screen interface or should I make compromises on the large interface to be able to run it also on the phone? A solution might be a completely seperate interface for the iPhone that would offer only some of the functionality of the iPad but I'm not sure I can pull that off.

Now, for the important part: Could you please give me some feedback what you like and dislike about the current user interface and how you would like to see it improve?