You can plan every "top level" path you'll ever want on the site from now until forever? Or do you mean planning as in plan to force account name changes on users when someone's username conflicts with a new feature name?

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account42 an hour ago | parent [-]

You could probably get away with banning all common english words as usernames if you wanted to.

	▲	nkrisc 27 minutes ago \| parent [-]
		Or put all user pages under some top level path and then you never need to ban anything as this problem becomes completely moot.