He's said something pretty similar about J: "I highly recommend that all programmers learn J. I doubt most will end up using it for daily work, but the process of learning it will stick with you. J is so completely different from everything else out there, and all your knowledge of C++ and Python and Scheme goes right out the window, leaving you an abject, confused beginner. In short, J will make you cry." (http://prog21.dadgum.com/48.html)

While I think multiparadigms are very practical, the easy availability of familiar approaches is a weakness when using them for studying programming.