namespaceDupes.php & cleanupTitles.php can be necessary when making certain kinds of tweaks to the system, but they're kind of opaque.
In addition to improving their CLI interfaces (eg T29048), I think it would be beneficial to give these a web UI interface which can let local sysops / bcrats / stewards (or whoever) find and clean up broken pages without manual intervention from server maintainers.
(For Wikimedia, this will mean less site-request bottlenecking: after a namespace tweak or other change that ends up causing problems, there'll be a larger pool of people who can fix it.)
A web UI will also be better at providing interactive controls, eg to do batch checks / confirmations / resolutions of ambiguous states.
Version: 1.18.x
Severity: enhancement