MB's left navigator hasn't been changed for a long time when it comes to its layout.
And now on Windows 10 the navigator looks a little outdated compared to other updated elements.
Recently I tried Groove. Nothing was special except its left sidebar. Maybe there's something to learn from it.
By default it shows icons only in left sidebar (with tooltip on the mouse over each icon). If you click menu icon at the top, then it opens the full sidebar. That's a brilliant approach because it gives a pretty clean look most of the time without losing functionality.
Why not adopt this and give MB a more modernized look to its navigator? endeavour1934 already provided Windows 10 style icons with his skins.
Of course MB has lots of nodes to display on one screen without scrollbar. It could display some key nodes by default, and make it customizable so that users could show their favorite nodes.