You’ll need to fork the main kwsys repository (linked in the MR) and make an MR for it. Brad will review it there. I suspect the changes aren’t as straightforward as they seem; that library supports dozens of platforms and I don’t know if std::codecvt stuff can be assumed to work on all of them. Once it is merged into master there, running the update.sh will bring the changes into your branch.
Agreed. I’d like to see vtkStdString gone as well (though deprecation is OK, I don’t think we should keep it around; it’s use has been discouraged for years).