Drupal is not intended for Single Page Apps. Drupal has never been, nor should, be a choice for lean startups to build their exit strategies upon. The community prides itself in producing quality open-source code for one of the strongest foundational CMS frameworks in history. When Trello is rebuilt it will not be on Drupal 8, nor Drupal 9 - nor should it be.
I’m not suggesting that keeping with current trends and languages in the industry is poor-form, but I am suggesting that pledging our Drupal allegiance to a singular framework is a bold step that will ultimately sever much of Drupal’s flexibility that we hold so dear. I’m proposing that Dries and the larger community aim our efforts to strengthening Drupal as a framework-agnostic endpoint. As Drupal developers we should focus on creating a Drupal ecosystem that thrives by itself. The more we tie ourselves to other frameworks and languages, the more we lose our identity. Before we know it Drupal 9 will just be a shell for Angular 4.