If your using a versioned codebase you likely don't want that anyway. Otherwise you'll have untested code on production, and you'll have to commit it to the project repository from production.

Normally you want all code changes to happen locally, and get tested locally, before they ever make it to production. Which means your client will need to get you to install the plugin.

It depends on the project and client though. There are levels of engagement that are a lighter touch, and in those cases you just accept the mess and risk associated with users managing plugins.