Follow-up from "Properly implement prepending for Concern"

The following discussion from !7079 (merged) should be addressed:

• @smcgivern started a discussion: (+3 comments)

  Should we propose this upstream?

My consideration:

• This should make ActiveSupport::Concern less confusing with prepend, so if people really want to use it, then I think this is a good fix.
• I never liked ActiveSupport::Concern and adding more stuffs to it will make people couple with it even deeper. (there is no changes between activesupport v4.2.10 and v5.2.1)
• I don't know how upstream will think about this, and I won't enjoy convincing them.
• This might not work with older Rubies. Last time I fixed something in rspec-mocks, but I broke Ruby 1.8.7 and they seem still want to maintain it.