I agree that without breakpoints set, Go is currently useless. I believe that you are proposing that it become a 'Start slide show' button, where a 'slide' is the execution of one statement.

I really like this idea. Like music or dance notation, a programs is a static representation of a dynamic performance.  An expert programmer, like an expert musician or dancer, can imagine a performance.  But without seeing a calculation performance, novice programmers may have trouble knowing what they are supposed to be doing.  For Python, calculation results are made visible by namespace bindings. 

Suggestions based on experience with automated slide shows:
* a user-settable delay between statement execution (possible 0).
* use space bar to stop and start
* allow single stepping while stopped, and space-bar restart after

A debugger-specific suggestion:
* step over functions whose code is not in a clean editor window (no unsaved edits)

try:
    filename = f.__globals__['__file__']
except AttributeError:  # builtin function or method
    <step over>
else:
    if filename not in filelist or buffer dirty:
        <step over>
    else:
        <step>

> trying to make a GUI program act like a command line program.
I don't think I understand that completely, except perhaps that the reason for the nested event loop is to avoid blocking the main event loop.  And maybe that you believe we can avoid the likely troublesome nested loop without blocking the main loop. (It does seem like judicious use of .after, commands, and callbacks should avoid needing a nested loop.)