Back in the Section 333 days (prior to Part 107), we were required to utilize the N# for registration which required the full "3-part paper form" which is a total pain in the tail feathers. Not only during the initial portion of the application (you could make no mistakes and if you did you had to start totally over on a new set of paper forms) but even more so if you wanted to UnRegister or transfer registration to someone else. I still have an N# aircraft simply because it contains my Area Code and Initials so it's "personalized", but it's out of service and I allowed Registration to expire but it's cool to have it as a "Conversation Piece".
N# is reserved for Special Use UAS and I doubt you'll get one approved now for Hobby or Part 107 operations if you try to do it from scratch. Even if you could, the real question is WHY would you put yourself through that hassle at this point. The Drone Zone is so quick, efficient, and SIMPLE it's silly to not utilize it now.