It should be possible to blacklist specific domains or regexes locally or globally for all wikis in a wiki farm. Recent forms of harassment consist on outing or doxxing individuals, their families, or both; by posting URLs to external sites where the harassed user is either depicted, or information about them can be found, etc. Sometimes the harassment consists on doxxing the invididual directly on-wiki without URLs.
Using SpamBlacklist when URLs are used is not adviceable because its contents are in a public wiki page for all to read and see. Moreover, users triggering the spam blacklist are told why via MediaWiki:Spamprotectionmatch.
Using TitleBlacklist has the same issues as spamblacklist. Is a public page, tells the user why (MediaWiki:Titleblacklist-forbidden-(?:edit|move|upload|new-account))
Using AbuseFilter will not be satisfactory either, because [at least on Wikimedia] there's no true global abusefilter that applies to all wikis. Moreover while private filters do exist, abusefilter-view-private is assigned to all sysops and some other groups not under NDA. T290324: Create Oversight-level abuse filters would be great though.
$wgSpamRegex can do what it is being requested; but the main disadvantage is that this needs a deployer to add/remove the offending regexes to the configuration, and in any case the user hitting the filter will be told exactly why (same as Spam/TitleBlacklist), which defeats the whole feature as it allows the doxxer to know what we're looking for to filter it and change the pattern to defeat our measures.
As such, it has become necessary to build a MediaWiki special page (either in core or as an extension) where we can blacklist specific "nonpublic" domains/regexes/patterns that ain't simple spam and are being used for threathen our user base.