I am not quite sure what the purpose of overhead monitors might be. There is not much use for this, other than an occasional effect here and there in some films. But for such a small effect such a big and expensive system, I don't see that becoming a big success. But I hope I am wrong.
Cinemas are predominantly a business. And I agree with Fred, sound has low priorities. I find it hard to find a commercial cinema that even has a decent 5.1 system. The audience does not seem to care a lot about the sound. I just had a revelation about this a few month ago. I went to see a film in a cinema that usually has a good sound system. Well the centre speaker was broke. So they used the right speaker as centre and panned the signal from the right speaker to the left speaker. So you had the stereo signal mono down mixed coming from the left and all the centre signal coming from the right. Plus of course noises coming from the surround speakers that where now totally unrelated to the front speakers. Of course it sounded horrible, but no one other than me even seem to have noticed that there was something wrong with the sound.
I complaint to the cinema and got a very polite answer from them. But two month later I was in that cinema again, thinking that they must had mixed by then, but it wasn't fixed. Their calculation seems to be that 99% of people do not realise the difference between mono and 5.1. And as sad as it is, but they are probably right with this calculation. At least actively, 99% will not realise that there is something wrong with the sound. Of course the film experience will be worse, but they will just blame that on the film. So who is going to care about Dolby Atmo?