ayg wrote:

I wouldn't add this by default, but some good way of customizing the personal tools might be called for. Perhaps a system message?

robchur wrote:

MediaWiki has no concept of a private sandbox, nor any kind of sandbox. This would add superfluous clutter to the user interface. Recommend WONTFIX.

ayg wrote:

Yes, the sandbox specifically definitely should not be added to the default software, it's a basically Wikipedian convention. However, the ability to add arbitrary links to the personal toolbox might be useful, especially on a per-user basis (it is after all a *personal* toolbox) but also on a per-site basis. Currently it can be done with JavaScript, but that's not ideal for accessibility, etc., especially for defaults.

Perhaps there could be an equivalent of Mediawiki:Sidebar for personal tools, that would allow arbitrary links to be added to it.

Hmm, the original example in the task here, was resolved by the creation of https://www.mediawiki.org/wiki/Extension:SandboxLink
Any wiki can request that extension (using the process at https://meta.wikimedia.org/wiki/Requesting_wiki_configuration_changes )
and thus will be added to the existing list of wikis using it at https://noc.wikimedia.org/conf/InitialiseSettings.php.txt (ctrl-F for wmgUseSandboxLink)
That probably means we can resolve this task, as written?

If you want someone to build a custom UI that would make it easy for anyone to add arbitrary links to their individual personal-toolbar or sidebar toolbox, you should probably file it as a different task (or arguably, you could rewrite this task's title and description so that it's less abstract!).
Whilst I've got it open... Here's a handy link of examples of scripts that add items to the personal-toolbar or the toolbox: https://en.wikipedia.org/wiki/Wikipedia:User_scripts/List#Personal_toolbar_(top)