BAD NEWS!!! Kitware will deprecate Tcl/Tk support inside VTK, see announcement , and merge request
Extract from the announcement:
Hi, I've made an MR to deprecate Tcl for 8.1 and remove it for 9.0. There was discussion before the hackathon on it, but it seems to have been missed. Deprecating it is easy, but there are related modules which are now in question: ...