Genuine question: why would someone want to do this? Shortcodes work, and will be usable both within Gutenburg (oh, how I dislike the absurd pretentiousness of claiming the name of a world-changing pioneer for something so mundane as an evolution in an editor) and outside it. If you want to support people using Gutenburg, and people not using it, and not to maintain two piles of code, then why bother with a block?