SpecialWikibaseQueryPage is abusing inheritance badly and is violating the
SRP. It has been identified as one of the more problematic pieces of code
in Wikibase. QueryPage itself also violates the SRP rather clearly. Query
construction and output formatting belong to different actors. Plus if one
derives from it, you'll again have inheritance for code reuse. And that is
keeping quit about the problems all special pages have since the special
page system is badly designed.
Unfortunately we currently have to deal with this legacy API, and thus have
to create a special page. Creating a direct derivative from SpecialPage
itself that just delegates to objects of which we can control the lifecycle
is one way to minimize dependencies on this legacy API and to mitigate the
problems it creates.
Jeroen De Dauw
Don't panic. Don't be evil.