Part of that functionality is already built in. If the user is logged in, then the form attempts to get the first name, last name, and email from the user’s account/profile. However, first name and last name are not usually created via the normal registration forms, so those fields might not be present. After they fill out the sign-up form the first time while logged in, all those fields are saved to the user’s meta info so they won’t have to fill it in the next time.
So, at least that part of what you want is already in the plugin, but we allow them to modify it in case they want to use a different contact phone number or have changed email, etc… that was the way we set it up for our PTA site, so that’s the way I released it. Also, there may be item details that they need to enter, so we can’t skip the sign-up form completely.
To skip the form completely, or to disable the inputs once all that info is in the user’s account, would require some custom programming, so I will keep this open as a feature request.