I was thinking that, unless they succeed in some good stunt casting (and Dan Stevens is not going to sell tickets, although he may be good in the role),I am just thinking that it will have run its course. I have never had the impression that it was the hit that South Pacific started out as, and by September I think it would have run about the same time as TKAI.
These things may just too well known (hit movies, regional productions over 60 years, touring companies, summer stock, high school and college productions (my high school did South Pacific 50 years ago) to ever enjoy the type of long runs that we have become used to (see different subject: Why Did Memphis only run Three Years). I can actually only think of four revivals that had serious long runs: Chicago, (which received rapturous reviews, didn't have the over-exposed issue before opening, and would probably called it a day in its fourth year, had it not been for the boost it got from the wildly successful movie); Grease (nostalgia); 42nd St. (which, of course, ran 3 1/2 years, but lost money); and Guys and Dolls. Even with G&D, it was a monster hit when it opened because of the similarly rapturous reviews, but really lost steam pretty quickly in its second year and didn't make it to three full years. That last one in particular told me that revivals as a rule are just not going to run that long.
One more: if I go back almost 50 years, there was No No Nanette, which ran less than 1,000 performances, but that was an amazing run in those days. Also, most audience members knew nothing about that show other than its title, because there was no movie (or if there was, it never lasted the public eye); there were no college productions; etc. So,I don't think it really counts; if was more of a one-off phenomenon.
So, minus successful stunt casting, I say September, unless LCT has no concrete plans yet, in which case maybe next Christmas.