Speaking from experience,

having someone copy you and imitate you is actually quite creepy.

Why would you want to imitate someone else or copy them?

Not just trying to imitate my appearance but also stealing my unique name, namesday and Twelve's Guardian.

Lastly, some people can and do feel their character designs are an extension of themselves, and or a form of art. It also is potentially an avenue of which one could be considered breaking the terms of service.

3.4 Impersonation. You may not impersonate any person or entity or fraudulently hold yourself out as a Square Enix employee, representative, or any other Square Enix-connected person or being affiliated with any such person or entity. This means you cannot log into someone else's account, or deceive or mislead other people as to your identity. For your own safety, we encourage users to safeguard their privacy, remain anonymous, and never give out personal information to other users.

You dont need to copy anyone, and I'm confident Square-Enix will not, and also should not, implement such a feature.