For me for Tcl to be relevant again its needs

1. a Package Manager (they sort of already have one called TEA, but its not active as far as I know)

2. an IDE or a good modes for the popular editors (VS Code, Emacs, Vim, Sublime Text)

For a UI language the absense of a good IDE or editor modes is very strange, you would expect that a Tcl/Tk IDE written in Tcl/Tk (one that also serve as UI framework or scaffolding for other apps) would be its killer app, but there isnt one