For me concepts are a joke. They have been in development, like, forever (heck, even perl6 project got started and was released in the meantime!), they are hugely polarizing for the committee and the supposed benefits are, well, lofty. In the meantime everybody just got better at spotting common patterns in template error messages. Is there a point beyond which everybody will essentially give up or is it a point of honor to bring them into the standard?