The vast array of Schemes available is part of what made me eventually land at Tcl and just dig in there.
Tcl/Tk is still an unrivalled way to prototype a GUI -- and with Snit megawidgets, it's almost like programming a modern JavaScript component framework like React.
Completely agree about the utility of Tk. I remember reading somewhere that HTML/CSS widgets were influenced by Tk. Don't know how true that is but I can see how it could be.
(I actually tried to retrofit some of CL in Tcl, heh; https://wiki.tcl-lang.org/page/q3cpma)