If you have a Tumblr blogblog (versus network, site), can you help test an updated version of the importer? It uses their OAuth APIAPI An API or Application Programming Interface is a software intermediary that allows programs to interact with each other and share data in limited, clearly defined ways., which requires you to create an application. It’s simple and the pluginPlugin A plugin is a piece of software containing a group of functions that can be added to a WordPress website. They can extend functionality or add new features to your WordPress websites. WordPress plugins are written in the PHP programming language and integrate seamlessly with WordPress. These can be free in the WordPress.org Plugin Directory https://wordpress.org/plugins/ or can be cost-based plugin from a third-party walks you through it. Here’s the ZIP file to the beta version. You can report bugs on #22422.

Edit: The plugin has been released, the beta is over: https://wordpress.org/extend/plugins/tumblr-importer/