In T233099 we made it so that extensions can extend the page previews extension with custom preview types (documented at https://www.mediawiki.org/wiki/Extension:Popups#Extensibility)
One caveat with using custom types is that the tooltip does not get stripped on hover automatically meaning the tooltip and page preview show at the same time:
Fixing this requires revising the way we allow the user to disable/enable preview types using the settings cog at the bottom of the page. See this comment: https://github.com/wikimedia/mediawiki-extensions-Popups/blob/master/src/changeListeners/linkTitle.js#L50