Musicaldudepeter said: "I think given Sher and LCT's history with O'Hara, she would have been announced with the production announcement, so I think it's safe to assume it won't be Kelli. Judging by what she's been saying in recent interviews, it seems she's not content with simply churning out revival after revival. King & I was the culmination of that period for her and she capped it off with a perfect Tony win. I think the next musical she'll do will likely be an original one written for her. I think she's more interested in pursuing other concert-based projects and operatic roles that are suitable for her right now… She's also probably anxious to be with her family, and the thing about opera is the schedule is definitely not as full on as Broadway, so she can afford to do it on her own terms. "
Your thoughts about Kelli's career and the direction that she would like to go in now, as well as concerns about her family, make perfect sense and I would think the same. But if you listen to this interview, it turns out that we are mostly wrong. Original vs. Revival. Makes no difference to her. She approaches the revivals as if they were new productions that she, and Bart, want to make relevant to now. Hard to believe, but she never saw any film or production of The King And I before starring in this production, and never listened to Gertrude Lawrence on the cast album.
She and Bart set out to address "now" with each production. Now that she is older she wants every project she undertakes to have meaning for her. The reason for her commitment to The King and I was to instruct theatergoers on the themes of equality of women in society and the education of women. The main reason for doing a My Fair Lady revival, even more than her love for the score, would be to raise the subjects of the class system in our society and the independence of women in society. This is, of course, what Shaw addressed when writing the play, but they want to be sure that these cultural issues are presented in a way that they are relevant to "now".
Kelli also discusses her need to be there for her young children. Again, it somewhat surprised me to hear her say that she doesn't mind the eight shows a week, that she feels rather grounded in the routine, and that it only takes up three or four hours of her day.
My final impression, for whatever it's worth, is that she should would love to play the part but just assumes that she is too old. (In her favor, perhaps, as I'm sure has already been mentioned, Shaw wrote the play with his soon-to-be good platonic friend Mrs. Patrick Campbell in mind, and she originated the role in 1914 at the age of 49 and performed Eliza in a London revival at age 55.)