Hey Dmytro,
I think the idea of allowing some conversions to be non-narrowing is fine in principle; there are some parts that really need elaboration though.
I'm not really sure what the motivation here is for instance. The examples with your wrapper class templates are contrived because in generic code, you don't use list-initialization due other issues with narrowing conversions and due to std::initializer_list constructors. You list forwarding as a motivation, but perfect forwarding should never use list-initialization in the first place.
I also don't find the argument that a library solution cannot work convincing. List-initialization cannot cover loss of information between possible future standard library types like std::big_int, between existing types like std::complex, etc. There is no customization point to define certain constructors as narrowing or "list-init-deleted", so preventing information loss via list-initialization is incredibly half-baked. It may have been a mistake in hindsight.
What I would like to see in the paper above all else is a concrete real-world motivating example.