Hi. I can help you out.
Case 1
Create the html mail / newsletter on backoffice
I assume you're using simplenews module to create the newsletter.
you will be using simplenews_content_selection module to allow the user to create a newsletter.
Case 2
Create the html mail front frontend.
Well, this would be tricky. With a few lines of jquery you'd need to pass / request the node selection and create the body of the html mail in "runtime". (There would be a need to perhaps have a inputtype for dynamic recipient/send to?) Then "call" the mailsender function with some ajax, to perhaps a custom module. just a line to execute the mail out.
Would this make sense?
I am interested.
Regards