It's a good article but it seemed to leave some questions unanswered for me. (1) Why isn't TFO enabled by default? I guess the answer involves bad middleboxes

It's a good article but it seemed to leave some questions unanswered for me. (1) Why isn't TFO enabled by default? I guess the answer involves bad middleboxes, but then how is the client/server meant to know any better, and isn't the very conservative fallback supposed to mitigate that? (2) What should the queue size be set to?