Foi ótimo enquanto durou, pessoal. O Dropbox terminou o suporte para servir arquivos HTML a partir de hoje para usuários do Basic.
Dropbox Basic (free) users: Beginning October 3, 2016, you can no longer use shared links to render HTML content in a web browser. If you created a website that directly displays HTML content from your Dropbox, it will no longer render in the browser. The HTML content itself will still remain in your Dropbox and can be shared.
Dropbox Pro and Business users: Beginning September 1, 2017, you can no longer render HTML content.
de link