Hi Stefano, I look forward to seeing this option.
Quickly, I would like to see the ability of the subscriber to pick the category when enrolling. On the Newsletter config page, I would like to see a Category include section, not just the Category exclude, as if you add a new Category, do not want to have to go to all of the newsletters and mark the exclusions.
If I understand correctly, you will add a multiple newsletter capability with the newsletter allowing for a particular category only. It will send only the latest posts and the widget will allow for the subscriber to pick that category (or newsletter) and the subscriber will also be able to modify their profile to add or delete said newsletters.
Hope this is along the lines you are thinking.
Thanks,