I recall us doing this a couple of times when I was at Etsy (2012-2015). I think we did it with Github as well.
The thing to keep in mind is that accepting non team members and getting them meaningful work to do was already part of Etsy's culture. New engineers would bootcamp with a team for a couple of weeks when they joined. So the culture was already set up for this - managers and team members knew what to expect from a teammate who may not be a domain expert.
I think the way to start a program like this is to start with an internal bootcamping type program and learn and make mistakes through that.
The thing to keep in mind is that accepting non team members and getting them meaningful work to do was already part of Etsy's culture. New engineers would bootcamp with a team for a couple of weeks when they joined. So the culture was already set up for this - managers and team members knew what to expect from a teammate who may not be a domain expert.
I think the way to start a program like this is to start with an internal bootcamping type program and learn and make mistakes through that.