One final statement regarding making a breaking change here: You should
consider that the packages orderless etc are fairly new and still have
breaking changes from time to time, so even if these configurations are
widespread or see growing adoption, this should not hold you back from
making a breaking change. I will then promptly adapt the documentation
of these projects and add a warning note, which will soon propagate to
the users who use Emacs master, which is still young in the development
cycle. Of course my statement applies only if the aforementioned are
truly the only widespread packages affected by this.