There doesn't seem to be a uniform way to query or set page properties in MW. Cindy has already developed an interface for [[ https://www.mediawiki.org/wiki/Extension:Semantic_Title | SemanticTitle ]] that she would like to include in core.
I've found a few extensions that use the page_props table and could probably benefit from a uniform way to access the information. I think this shows a use that needs to be met. The extensions are:
* [[ https://github.com/wikimedia/mediawiki-extensions-ApprovedRevs/search?utf8=%E2%9C%93&q=page_props | ApprovedRevs ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-BlueSpiceFoundation/search?utf8=%E2%9C%93&q=page_props | BlueSpiceFoundation ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-ConventionExtension/search?utf8=%E2%9C%93&q=page_props | ConventionExtension ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-GoogleNewsSitemap/search?utf8=%E2%9C%93&q=page_props | GoogleNewsSitemap ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-Disambiguator/search?utf8=%E2%9C%93&q=page_props | Disambiguator ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-PageSchemas/search?utf8=%E2%9C%93&q=page_props | PageSchemas ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-SemanticDrilldown/search?utf8=%E2%9C%93&q=page_props | SemanticDrilldown ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-TemplateInfo/search?utf8=%E2%9C%93&q=page_props | TemplateInfo ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-TemplateData/search?utf8=%E2%9C%93&q=page_props | TemplateData ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-WikiBase/search?utf8=%E2%9C%93&q=page_props | WikiBase ]]
* [[ https://github.com/wikimedia/mediawiki-extensions-WikiData/search?utf8=%E2%9C%93&q=page_props | WikiData ]]