The name for that fork is TUI (Tcl User Interface), but up to now 90% of original code is still used (for the modules taken over, which is only a smaller part of the full implementation about 20-25%). There have been about 25.000 lines of the source code adapted for TUI usage (not much had to be modified).
After that the implementation of “derived classes” has been started to build a button widget with YUI functionality.
The next part (still in progress) is the implementation of a Tktable widget. There exists a datatable implementation, but that has only title lines and there are always at least one title line. Titlecols functionality is missing completely, and also the tag functionality is missing, so there has been started an implementation of a Tktable widget based on the TUI functionality and similar to the datatable implementation of YUI. As in YUI scrolling will be done with a plugin attached to Tktable widget. Other widgets like Tree, panedWindow, ScrollableFrame etc. will follow.