You omit to provide your conceptual definition of identity.
It is critical to do so to begin to understand the boundaries within which your hopes for SSI might play out if we're very careful, and by corrolary those aspects of the human condition and community without for which it might be / will be deeply harmful.
Uber and Couchsurfing are different contexts. Reputation "porting" between contexts inevitably leads, I think, to non-contextual reputation. And non-contextual reputation is an unmitigated evil. What am I missing?
Disposability is one way to describe a persona fading with irrelevance. For example, the personae I may have lived through as a teenager are entirely redundant to me in my 40s.