There is no relationship yet.  Boost.Text is an experiment meant to gather feedback, which will in turn drive the standardization effort.  I believe all large libraries should have Boost-equivalent visibility in the C++ community before being standardized.  That being said, some of my fellow SG-16 members (that's the committee's Unicode Study Group) have started proposing some actual APIs for standardization.  The first of these is the most low-level: transcoding (see http://www.open-std.org/jtc1/sc22/wg21/docs/papers/2019/p1629r0.html ).  JeanHeyd's approach is more ambitious than mine -- I really only care about Unicode.  His proposal covers conversions among all possible encodings, including an API that lets users add implementations for the encodings they care about that are not covered by the standard.

There are no other in-flight Unicode API proposals that I'm aware of.

Zach