It would be fairly complex to implement this, as the changes not only have to be reflected in the registration form, but also in the profile viewing code and profile editing code (and really anywhere in the system that uses the $user->getInterests() or setInterests() function). Plus, you'll have to be comfortable working with PHP and Smarty templates, and finally these changes will likely make upgrading rather difficult. But, I'll give a quick rundown of some of the files you'll have to work with and I hope it helps!
For registration, the relevant files are templates/user/register.tpl (which displays the registration form), and classes/user/form/RegistrationForm.inc.php (which tells the registration template to be displayed and assigns data to it, i.e. this is where you would use $templateMgr->assign() to send your journal sections and reviewing interests to the template, which you then would iterate through in the template). When the form is submitted, the function registerUser() in pages/user/RegistrationHandler.inc.php receives the data. Here you would have to parse the review interests form data, which will likely be some sort of array, and convert it to a string so the $user->setInterests() function can handle it. You'll then have to edit the profile display and editing code (classes/user/form/ProfileForm.inc.php and templates/user/profile.tpl) to accommodate these changes to registration.
I'll leave it at here for now, to see if you'll have the resources to handle all these modifications and if you have any specific questions.
Public Knowledge Project Team