Please note that you can already do this in a round about way.
Admin can clear any signups from the admin dashboard.
Admin, or any other user, can sign up anybody on the front end form. If you are logged in, it will pre-fill your information, but you can override any of the fields, allowing you to sign up someone else. If you enter the other person’s email address when you sign them up, they will get a confirmation email immediately, as well as reminder emails if you have reminders set for the sheet.
So, all of the above is possible, just not all for the admin dashboard right now. The only catch, is that if you are logged in when you sign someone else up, it will still put that signup as belonging to your user ID (the user that is logged in). To work around that, you should be logged OUT of the site, and then when you signup somebody else, it will try to match the email you enter to a user account. Then, that person will be able to see the clear link on the signups list.