License incompatible with PyQt5
As Bastian Germann reports here and here, the current license of TortoiseHg (GPLv2-only) is incompatible license with the currently version of PyQt5 (GPLv3).
As he points out, apart from relicensing thg, it should be possible to convert the source to PySide2 or QtPy, which have licenses compatible with thg (making relicensing a less urgent issue).