Ruby master - Misc #16645: Non-warned change of behavior in 2.7 for non-symbol keys

I can not answer your question but I believe matz mentioned the change several times in different
talks before. So a deprecation phase makes no real sense, unless matz and the core team wants
to postpone the change past ruby 3.0 - but I think it was decided that keyword arguments will be
just about the only backwards incompatible change before. If you look at the issue tracker,
you will always have people who want more deprecations and more changes, and people who want
less - e. g. the discussion about frozen strings by default, where headius (and probably others)
would like a change in ruby 3.0 already. ;) (It's a decision either way and I think for keywords
the decision has already been made months before to change this in 3.0, so a deprecation phase
would make no real sense to me, IMO, in this regard.)