A lot of questions.
Certainly this forum is also about AWES that are not too much represented elsewhere.
But Yo-Yo is studied by @tallakt (KiteMill), @Kitepower, @rschmehl even when other aspects than the conversion system itself are detailed. Myself I experimented Low radius loop for Yo-Yo use.
For what I investigated in different AWE method, I have not still seen any robust way for success, but this is not a proof that success is not possible.
For both Yo-Yo and flygen, rigid wings work well at small scale. But for large scale the weight should be drastically reduced. So a work for lighter structures is needed.
For flexible wings, the control accuracy and the lifetime should be improved.
And also carousels comprising NTS X-Wind could be more investigated, with several equipment,comprising rigid or flexible kites, or sails.