Imagine being able to port your Uber or Lyft rating and comments into your new Couchsurfing account — The cultural premises of these groups are different, but if a trusted Couchsurfing node says “hey, that info can still help us get to know a person faster”, then you don’t have to start from scratch building a reputation on Couchsurfing.
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?