The number 1 usability gotcha (by far) on our cryptpad instance is the "safe link" feature, which regularly causes confusion and frustration. Our instance is managed collectively, and we would clearly prefer unsafe links to be the global default, in order to reduce friction for newcomers.
However, this is not possible today; each user has to set the option independently, and regularly reminding our users to use the "share" button or change their settings feels like an uphill battle.
Thus: an admin-level setting to change the default would be very welcome.
I understand that this wouldn't change the setting for existing users (only for new accounts), but it would be an improvement already (we would only have to pay the one-time cost of telling current users to change the setting).