Infrastructure-wise, the FOSS wordpress.org that you self-host isn't quite the same as the massively multi-tenant wordpress.com service run by Automattic. Your

Infrastructure-wise, the FOSS wordpress.org that you self-host isn't quite the same as the massively multi-tenant wordpress.com service run by Automattic. Your comment seems to be about the former, but this announcement is about the latter. In other words, they're proposing a migration of some unspecified portion of Tumblr to re-use existing infrastructure/code/services that power the wordpress.com hosted service. They're not proposing somehow moving 600 million Tumblr blogs to individual FOSS wordpress.org instances; that indeed would make no sense whatsoever.