Casting gem usage in Rails 4/Ruby 2 vs. Rails 4 push for concern usage/Rails delegation

Just read about the Casting gem:

What are the Rails core team’s opinions about using Casting vs. ActiveSupport::Concern usage, Rails delegation, etc.?

Seems to me like AS::Concern and Casting deal with significantly different use cases: modular functionality at class-load time vs. modular functionality at runtime.

Also, the benchmark noting the 100x speed difference compared to standard method dispatch is pretty hair-raising.

--Matt Jones