"Bernadette would SLAY "If he Walked Into My Life"!!!"
I think she might have slain it 15 years ago at the latest; at 68, her voice is, I believe, no longer sufficiently strong or flexible to sing and act this role even 6 times a week.
Don't you think Mame should pass for no older than 40, at least during Act I? And perhaps there would be no commercial Broadway revival unless the actress hired was a genuine star to more people than just a few thousand rabid musical theatre devotees? That said, here are thoughts about actresses suggested above:
Jane Krakowski - 47, somewhat well known, not a very strong voice, would be a rather trashy/sexy Mame;
Jessie Mueller - 33, good voice, difficult to glam up (as Clear Day showed), not much of a national star;
Kristen Chenoweth - 48, soprano not belter, terribly short, known to America primarily from supporting/bit roles;
Christine Ebersole - 63, soprano, not a star;
Christine Baranski - 64, belter/soprano, moderately well known, less a leading lady then character actress;
Christine Andreas - 64, soprano, not a star;
Bernadette Peters - 68, voice very delicate these days;
Donna McKechnie - 73, belting soprano, not a national star;
Patti LuPone - 67, still in great voice, short, stout, would be a sort of Long Island Mame;
Beth Leavel - 60, not famous;
Nancy Opel - 59, not famous;
Imelda Staunton - 60, slightly known to US audiences, generally plays frumpy/dowdy, but a terrific actress.