Fluxbox is still around. To install on Ubuntu:

sudo apt install fluxbox

So it's available as an option from the command line and then you could log out, choose the fluxbox environment and then log back in.

I think Fluxbox is a little too "minimal" to be included in the Traditional Desktop Metaphor. Right clicking on the desktop to get a menu isn't intuitive for most people (though it definitely has it's strengths and is super fast because nothing shows on the screen unless you want it to).

Thanks for commenting!