When will fresh expressions join the proper church?
As they mature, fresh expressions become proper church. Imagine a group of congregations of which some are traditional, perhaps meeting in a chapel or parish church, and others are fresh expressions of church, perhaps meeting in a café or skate park or school, or maybe over the internet. Both 'types' of church are real.
Fresh expressions of church may need to develop some aspects of their mission and ministry to become mature church, but just as a baby is a proper human so fresh expressions are proper church.