Miranda warnings also cue a person that custody has commenced. Without the warning, it can be hard as hell for anyone to determine whether they are "free to leave".
True, but there are some situations that are still defacto custodial, just not custodial for purposes of Miranda, at least not under the federal constitution.
There is NO Constitutional need to abrogate Miranda, and a case by the SC several years even spoke of stare decisis, and they refused to overrule themselves.
Why not just UNincorporate the Bill of Rights, as it was in Barron v. Baltimore, maybe Holder would like that??