Sorry to disagree 
What you are exposing here is YOUR view of how you like to use folder tree, tabs, file pane and viewer pane.
I do not share that view at all : most of my layouts do not even show the folder tree, as they have all the required tabs for the workflow they are designed to address opened (single pane for some layouts, dual pane for most of them), and some have 15+ tabs opened by default, the viewer pane is closed most of the time (even if I have a button to toggle it on and off), etc ...
Having the opened tabs on the left is not getting closer to the underlying structure of a system as the system does not start by the specific folders you are working with at a desired time.
To be clear, I'm not saying you should change the way you operate : do what feels right to you. And I'm not saying my way is the way neither. My point is we all have preferred ways depending on our workflows and approach to them.
Nevertheless, there might be something that you can do : make a toolbar with GO TABLIST=namesonly that you put on the left of the folder tree. It will display the names (e.g. the folder name) of every opened tab in the active file display. You will not get fancy tab coloring though.
If your tabs are mainly static, you could also make a custom toolbar with "shortcuts" to your predefined tabs (with GO commands pointing to your standard/favorites folders), but it won't be dynamic (meaning, if you change the folder in one of the tabs, this will not follow along, whereas the GO TABLIST will).
And for the possibility of a new option for the location of the tabs, I will let GPSoftware team answer, since in the end, if I can keep it where it is now, it's fine for me.