Two things:
1) Cosmetic-only issues on Arch Linux with the tkinter gui: The "Clear All" button overlaps the "Select All" button and obscures part of the text. And the initial width of the widget does not allow all of the text for the options to be seen. Neither of these are deal-breakers, of course.
2) A little more serious ... many of the options result in destructive damage to the nav document of EPUB3s. You may want to do a quick check of the EPUB version and abort on EPUB3s if your plugin not prepared to support them at this time.
Returns as a unicode string the epub version ("2.0" or "3.0") of the current epub as determined by the version attribute value on the OPF package tag (first available in Sigil v0.9.3).
You can also parse the value of bk.getpackagetag() for the "version" attribute if you want to check the epub version in versions of Sigil earlier than v0.9.3.