Just because a service has a feature, doesn't mean a user has to use it. At its core, Twitter remains a 140-character-update service. (And no Leo Babauta, Twitter will never go beyond 140 characters because of the SMS-length limit.) And I fail to see what decentralising Twitter has to do with keeping it simple.
It's already possible to send tweets which would overflow an SMS. Twitter limits tweets to 140 characters UTF-8 characters, which can be multibyte. SMS is 140 8-bit chars.