The idea on using Gutenberg for all kind of form fields in WordPress is amazing. It truly is. The problem is when will it available? As Justin said in the article, 5 years consider a fail.

As the Meta Box's author (a custom fields plugin) and a follower to the Fields API, I feel the Fields API is more ambitious than what's said in the article. It shares some similarity with the Gutenberg. But it's deeply about the data, which is more about the storage and structure. Gutenberg is more focusing on the content (which is HTML & text) at the moment, and it has little support for custom data storage & structure.

I hope this can change in the future. But after the 2nd and 3rd phases, do we have enough time to get to that point within 5 years? I doubt that.