I was a big Tcl user between 1999 and 2002, our startup was an heavy user, however the experience of slowly replacing Tcl with C code, made me never choose languages without either JIT or AOT compiler ever again, other than for scripting tasks.
Maybe now is a good time to re-examine those assumptions and re-evaluate those priorities.
At a time when Electron is the cross platform UI toolkit of choice, Tcl/Tk seriously deserves a second look.