I see there is a User-Definable ToolBar (quick launch), but it is relegated to the tail end of the Command-Line bar.
I also see it's possible (as far as I can tell) to completely customize the Function/Button Bar (on the bottom) --- although I don't see how you can customize the context-sensitive nature of the Function/Button Bar - e.g. what is shown when Ctrl or RButton is pressed.
Multi Commander has internal scripting, and what appears to be access to internal commands.
Everything seems to be in place for the ability to have custom Tool Bars ... is that feature on the horizon at all? I don't see it requested, nor in the combined list of feature requests.