I have near zero experience with TCL. In the late 90s when I started using Linux it was already considered old; I had one program that used it, a Tk-based AOL Instant Messenger client that was, admittedly, the nicest piece of Linux GUI software I had.
TCL is almost gone today EXCEPT in the Verilog community, which uses it religiously because it's a single language they can use both for build scripts (because it's designed as a scripting language) and as a template language (it can do that too).